[compiler] Phase 1: Add error accumulation infrastructure to Environment

[josephsavona]

Add error accumulation methods to the Environment class:

• #errors field to accumulate CompilerErrors across passes
• recordError() to record a single diagnostic (throws if Invariant)
• recordErrors() to record all diagnostics from a CompilerError
• hasErrors() to check if any errors have been recorded
• aggregateErrors() to retrieve the accumulated CompilerError
• tryRecord() to wrap callbacks and catch CompilerErrors

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• [compiler] Update docs with fault tolerance summary, remove planning doc #35888
• [compiler] Fix Pipeline.ts early-exit, formatting, and style issues #35884
• [compiler] Rename mismatched variable names after type changes #35883
• [compiler] Remove local CompilerError accumulators, emit directly to env.recordError() #35882
• [compiler] Remove tryRecord, add catch-all error handling, fix remaining throws #35881
• [compiler] Cleanup: consistent tryRecord() wrapping and error recording #35880
• [compiler] Add fault tolerance test fixtures #35879
• [compiler] Phase 3: Make lower() always produce HIRFunction #35878
• [compiler] Phase 8: Add multi-error test fixture and update plan #35877
• [compiler] Phase 4 (batch 2), 5, 6: Update remaining passes for fault tolerance #35876
• [compiler] Phase 4 (batch 1): Update validation passes to record errors on env #35875
• [compiler] Phase 2+7: Wrap pipeline passes in tryRecord for fault tolerance #35874
• -> [compiler] Phase 1: Add error accumulation infrastructure to Environment #35873