refactor(config): replace frozen protobuf config with plain Go

[Cianidos]

Closes #143

Replaces the frozen protobuf application configuration types under pkg/common/proto/stroppy with plain-Go structs and enums in a new pkg/config package. The protobuf/gRPC dependencies for YDB and OTLP remain.

Acceptance criteria

• Plain Go types for run / workload / driver / pool / logger / exporter / isolation — pkg/config defines RunConfig, DriverRunConfig, DriverConfig, PoolConfig, PostgresConfig, SqlConfig, InsertProgressConfig, GlobalConfig, LoggerConfig, ExporterConfig, OtlpExport, and the DriverType / ErrorMode / TxIsolationLevel / LogLevel / LogMode enums.
• Preserve JSON field names + strict unknown-field rejection — camelCase json tags are carried over verbatim; protojson is replaced by encoding/json with DisallowUnknownFields (internal/runner.UnmarshalStrict).
• Replace protojson / proto.Merge — explicit JSON decode plus a deterministic per-field merge (internal/runner.MergePostgresConfig / MergeSqlConfig) that only overrides non-nil fields, unit-tested.
• Source precedence + presence — optional scalars stay *T pointers; the typed precedence CLI > env > -e > typed config > config env > default is untouched.
• jsonschema from the Go contract — docs/jsonschema/run.schema.json is now generated by the reflection-based internal/jsonschema-gen (go generate ./pkg/config), with no stale proto/TS descriptions.
• Migrate runners / drivers / bench / tests — all call sites updated; bench.Run, Workload, and driver.Driver public surfaces are unchanged apart from the config type.
• Deletions — pkg/common/proto/stroppy (all .pb.go + .pb.validate.go + descriptors), dead runtime.pb.go value types (Value, Decimal, Uuid, DateTime, DriverQuery, stats, etc.), pkg/utils/protovalue, pkg/utils/protoyaml, pkg/common/logger/proto.go, and the protoc-gen-validate dependency are removed.
• YDB/OTLP dependencies kept — google.golang.org/protobuf and google.golang.org/grpc remain (indirect) for those external protocols.
• Golden tests — accepted and rejected JSON (unknown fields, wrong types) in pkg/config/config_test.go plus the merge unit tests in internal/runner/merge_test.go.

Migration notes (v5 → v6)

• The config file JSON shape is unchanged: existing v5 stroppy-config.json files load as before with the same camelCase field names.
• -D/-d driver options keep identical precedence (-D postgres.* still overrides -D pool.*).
• k6Args / k6Config remain accepted-but-inert (they had no effect already).
• The frozen .pb.go config types are gone; any out-of-tree code importing pkg/common/proto/stroppy must switch to github.com/stroppy-io/stroppy/pkg/config.

Verification

• make build ✓
• go build ./... ✓
• go vet ./... ✓
• full go test ./... ✓ (all packages green)
• go test -race on every migrated package ✓
• gofmt clean; go mod tidy compiles with YDB/OTLP still importing

Note: the repo-wide make tests (-race + coverage) times out at ~10 min in pkg/datagen/tpchgen (TestOfficialAnswersQ1Q6SF1, the canonical TPC-H SF=1 official-answer generator, which is untouched by this PR and independent of pkg/config); every migrated package passes -race individually.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: c2cb5785-87b6-477e-92c8-439bab60f6c4

📥 Commits

Reviewing files that changed from the base of the PR and between c338c2f and 1e98265.

⛔ Files ignored due to path filters (6)

• go.sum is excluded by !**/*.sum
• pkg/common/proto/stroppy/common.pb.go is excluded by !**/*.pb.go
• pkg/common/proto/stroppy/config.pb.go is excluded by !**/*.pb.go
• pkg/common/proto/stroppy/descriptor.pb.go is excluded by !**/*.pb.go
• pkg/common/proto/stroppy/run.pb.go is excluded by !**/*.pb.go
• pkg/common/proto/stroppy/runtime.pb.go is excluded by !**/*.pb.go

📒 Files selected for processing (52)

• .golangci.yml
• CHANGELOG.md
• cmd/stroppy/commands/help/topic_config_file.go
• cmd/stroppy/commands/run/metrics_test.go
• cmd/stroppy/commands/run/run.go
• cmd/stroppy/commands/run/run_test.go
• docs/jsonschema/run.schema.json
• go.mod
• internal/jsonschema-gen/main.go
• internal/runner/config_file.go
• internal/runner/config_file_test.go
• internal/runner/driver_file_config_test.go
• internal/runner/driver_preset.go
• internal/runner/merge.go
• internal/runner/merge_test.go
• internal/runner/run_config_merge.go
• internal/runner/run_config_merge_test.go
• internal/workloads/tpcc/params_test.go
• internal/workloads/tpcds/params_test.go
• pkg/bench/enums.go
• pkg/bench/metrics.go
• pkg/bench/metrics_test.go
• pkg/bench/query.go
• pkg/bench/runtime.go
• pkg/bench/runtime_test.go
• pkg/common/logger/proto.go
• pkg/common/proto/stroppy/common.pb.validate.go
• pkg/common/proto/stroppy/config.pb.validate.go
• pkg/common/proto/stroppy/descriptor.pb.validate.go
• pkg/common/proto/stroppy/run.pb.validate.go
• pkg/common/proto/stroppy/runtime.pb.validate.go
• pkg/config/config.go
• pkg/config/config_test.go
• pkg/driver/csv/driver.go
• pkg/driver/csv/driver_test.go
• pkg/driver/csv/run_query.go
• pkg/driver/dispatcher.go
• pkg/driver/insert_methods.go
• pkg/driver/insert_methods_test.go
• pkg/driver/mysql/driver.go
• pkg/driver/noop/driver.go
• pkg/driver/noop/insert_test.go
• pkg/driver/picodata/driver.go
• pkg/driver/postgres/driver.go
• pkg/driver/postgres/pool/pool.go
• pkg/driver/postgres/pool/pool_test.go
• pkg/driver/postgres/tx.go
• pkg/driver/sqldriver/config.go
• pkg/driver/sqldriver/tx.go
• pkg/driver/ydb/driver.go
• pkg/utils/protovalue/value.go
• pkg/utils/protoyaml/protoyaml.go

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/issue-143-plain-go-config

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[Cianidos]

Review blocked: maintainer decision required

Independent code/config/runtime reviewers and an adversarial verifier tested this PR after merging current main locally. Full build, lint, race tests, and PostgreSQL Docker paths passed, but the config migration has verified compatibility defects. No integration commit was pushed.

Decision required: legacy protobuf field names

v5 accepts both canonical lower-camel names and protobuf source names such as driver_type, bulk_size, max_conns, run_id, log_level, stall_after, and no_steps. This PR accepts only canonical camelCase.

Both outcomes are valid but functionally different:

1. Preserve v5 aliases: add exact, collision-aware normalization for every former protobuf source-name alias at every nesting level, and reject canonical/alias collisions.
2. Make v6 camelCase-only: explicitly document this additional breaking change in changelog/help/schema guidance and add comprehensive rejection/migration tests.

Issue #143 permits v6 breaks, while this PR's changelog says existing v5 files continue to load and names only global.seed as divergent. That does not determine which policy is intended. Please choose one before this PR is merged.

Reproduced defects to fix after that decision

• Nested strict JSON validation regressed. Duplicate nested keys such as two drivers[0].url fields now silently use the last value; wrong-case keys, null driver entries, null map/list values, and nested null strings are also accepted/coerced where v5 rejects them. Strict validation must cover the full JSON tree and raw -d, report exact paths, and account for the alias policy above.
• Generated schema rejects valid config. docs/jsonschema/run.schema.json marks the root closed but omits accepted run and params properties. Restore the effective loaded-config envelope and validate the documented typed example in tests.
• ProtoJSON-compatible integers regressed. Existing quoted and integral-decimal/exponent forms such as bulkSize:"20" and pool.maxConns:"3" load on v5 but fail here. Preserve those forms for non-seed int32 fields while rejecting fractions, overflow, and malformed values; the documented numeric-only global.seed break can remain.
• Numeric logger enums regressed. v5 accepts known numeric ordinals for logLevel and logMode; this PR accepts strings only. Decode both defined symbolic names and valid ordinals, with boundary/error tests.
• Active project guidance is stale. AGENTS.md and Makefile still direct contributors to deleted pkg/common/proto/stroppy; point config guidance to pkg/config and describe remaining protobuf users accurately.

Representative evidence was reproduced against both current main (5005aa3) and the locally integrated PR (e6f1409), including real CLI config loads and schema validation. Per the sequential merge rule, this PR is skipped until the policy decision and fixes are addressed.