Pool EmitContext

[jakebailey]

These objects can be reused, which is good because we create one of them per file to emit.

[Copilot]

Pull Request Overview

This PR introduces pooling for EmitContext instances to reduce allocations by reusing contexts across files. Key changes include:

• Added sync.Pool and GetEmitContext/release functions in internal/printer/emitcontext.go.
• Updated consumers (emitter.go and test baselines) to use GetEmitContext with deferred release instead of NewEmitContext.
• Ensured EmitContext.Reset() clears prior state before returning to the pool.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/testutil/tsbaseline/type_symbol_baseline.go	Switched from NewEmitContext() to pooled GetEmitContext()/putCtx().
internal/printer/emitcontext.go	Introduced sync.Pool, GetEmitContext + release func, and Reset().
internal/compiler/emitter.go	Replaced NewEmitContext() with GetEmitContext() and deferred release.

Comments suppressed due to low confidence (2)

internal/compiler/emitter.go:136

• [nitpick] Consider standardizing the name of the cleanup function returned by GetEmitContext() (e.g. putCtx or releaseCtx) across the codebase to avoid confusion when reading pooled-context usage.

	emitContext, putEmitContext := printer.GetEmitContext()

internal/printer/emitcontext.go:47

• Add a unit test to verify that an EmitContext obtained via GetEmitContext() is reset to a clean state after calling the release function, ensuring no leftover state persists between uses.

func GetEmitContext() (*EmitContext, func()) {

[DanielRosenwasser]

Probably a good idea - any before/after numbers?

[jakebailey]

For the test runner, it accounts for 5% of the allocations (6179460), and with this PR just 0.1% (99838).