Synchronizer: Add consolidated sync report and --fail-on-error flag

[saidixith002]

Motivation

PolarisSynchronizer currently reports progress purely via interleaved SLF4J log lines (clientLogger.info/.error) scattered across each of its 9 sync methods. For any
non-trivial migration — hundreds of catalogs, namespaces, or tables — this is unreadable: there's no way to tell at a glance what succeeded, what failed, or how many entities
of each type were touched without grepping through thousands of log lines.

This is especially painful for automated usage (CI, cron-based backup/sync jobs), where the only way to detect a partial failure today is to scrape logs for ERROR lines.
There's also no way to fail a script/pipeline based on sync outcome — sync-polaris always exits 0, even if individual entities failed to sync.

Additionally, since the sync is designed to be idempotent (only the diff between source and target is applied), a fully-synced re-run currently logs each skipped entity
individually but never surfaces a summary — so a user re-running the tool sees no output at all and can't easily tell "everything is already in sync" from "something silently
didn't run."

What this changes

• sync-polaris now prints a consolidated synchronization report once, at the end of every run, instead of relying on interleaved logs. It summarizes, per entity type,
  how many entities were created, overwritten, removed, skipped (already in sync), and failed, followed by a list of failures with their identifiers and error
  messages:

    === Synchronization Report ===
    Principal:               3 created, 0 overwritten, 0 removed, 0 skipped, 1 failed
    Catalog:                 2 created, 1 overwritten, 0 removed, 5 skipped, 0 failed
    Table:                  20 created, 0 overwritten, 0 removed, 40 skipped, 2 failed

    Failures:
      - Principal 'alice': <exception message>
      - Table 'db.orders': <exception message>
    ===============================

Entity types with all-zero counts are omitted to keep the report scannable, and the Failures: section is omitted entirely when there are none.

• Adds a new --fail-on-error flag. By default, sync-polaris still exits 0 regardless of individual entity failures (preserving existing behavior: failures are logged
  and the run continues to completion). With --fail-on-error, the command exits non-zero if the report contains any failures. This is deliberately distinct from the existing
  --halt-on-failure, which stops the run at the first failure — --fail-on-error lets the run finish synchronizing everything it can, then fails afterward, which is
  generally what you want for a CI/cron job (best-effort sync, but still surface that something needs attention).

• Entities that were already in sync are now tallied under skipped rather than just being logged and forgotten. Without this, an idempotent re-run against an already-synced
  target prints an empty report with no === content in between, which reads as ambiguous ("did it even check anything?") rather than reassuring.

Implementation

• New EntityType, SyncOutcome, and SynchronizationReport classes (api/.../planning/plan/), mirroring the existing SynchronizationPlan/PlannedAction pattern
  already used elsewhere in this module rather than introducing a new abstraction style.
• PolarisSynchronizer takes a SynchronizationReport collaborator (constructor injection, same pattern as etagManager) and records an outcome at every
  create/overwrite/remove/skip site across all 9 sync methods.
• SyncPolarisCommand constructs the report, passes it into PolarisSynchronizer, prints report.render() via the existing console logger after the run completes, and
  returns exit code 1 when --fail-on-error is set and report.hasFailures().
• README updated with a sample report and documentation for --fail-on-error.

Test plan

• SynchronizationReportTest: recordSuccess/recordFailure target the correct cells, hasFailures() toggles correctly, render() omits all-zero entity types and the
  empty Failures: section, multiple failures render correctly, and SKIPPED is counted and rendered without being treated as a failure
• ./gradlew :polaris-synchronizer-api:test :polaris-synchronizer-cli:test passes
• Manually verified end-to-end against a local docker-compose Polaris source/target setup: first sync shows correct created counts; a second, idempotent run shows
  skipped counts instead of an empty report

[dimas-b]

Nice enhancement 👍 Thanks again for your contribution, @saidixith002 !

Just one minor comment.

[dimas-b]

Map.compute()?

[dimas-b]

@saidixith002 : please resolve merge conflicts

[saidixith002]

@dimas-b , Resolved all the conflicts. Please merge