fix(compiler): lower nested named functions as closures

[akonwi]

Summary

• lower nested named functions as lexical closure bindings
• preserve one declaration identity across direct calls, references, captures, shadowing, and recursion
• predeclare recursive closure slots and reject unsupported generic/static local signatures
• add checker, AIR, Go, span, documentation, and downstream regression coverage

Validation

• go test ./... -count=1
• go test -race ./checker ./air ./go ./lsp ./lsp/analysis -count=1
• go vet ./...
• gopls check on changed Go files
• LSP harness: 18/18
• website build
• downstreams: Tinear, Decode, SQL, Cooper

Fixes #480

[vercel]

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Project	Deployment	Actions	Updated
ard-lang-dev	Ready	Preview	Sep 7, 2026 4:58pm UTC