fix: replace finished() with writable lifecycle tracking

[trivikr]

This relates to...

• Hot-path listener overhead in lib/api/api-stream.js
• The existing TODO about avoiding stream.finished() in StreamHandler

Rationale

StreamHandler used stream.finished(res, { readable: false }) to observe completion of the user-provided writable. That helper is broader than this path needs and registers extra listeners, which adds avoidable overhead on a hot path.

This change narrows lifecycle tracking to the writable side only while preserving the behavior stream() depends on for completion, writable errors, and premature close handling.

Changes

• Replaced stream.finished() usage in StreamHandler with a small writable lifecycle helper that listens only for finish, error, and close
• Preserved premature close behavior by reporting ERR_STREAM_PREMATURE_CLOSE when the writable closes before finishing
• Preserved existing error propagation by aborting the request with the writable error
• Avoided re-destroying the writable with the same error after an 'error' event, which keeps existing error handling semantics intact
• Added regression coverage for premature writable close without an explicit error
• Added regression coverage for a factory returning an already-finished writable

Features

N/A

Bug Fixes

• Reduced listener registration overhead in stream() response handling
• Kept stream() callback and abort behavior consistent for writable finish, error, and premature close edge cases

Breaking Changes and Deprecations

• None

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

Posting as draft as this fix was generated by AI, and I don't fully understand the fix.
Maintainers can consider closing it and/or cherry-picking to a new PR.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.19608% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.92%. Comparing base (a434502) to head (ec6c073).

Files with missing lines	Patch %	Lines
lib/api/api-stream.js	90.19%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5001      +/-   ##
==========================================
- Coverage   92.93%   92.92%   -0.02%     
==========================================
  Files         110      110              
  Lines       35735    35781      +46     
==========================================
+ Hits        33210    33249      +39     
- Misses       2525     2532       +7     

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