stream: uncork fromWritable writev on chunk error

[trivikr]

Fixes fromWritable().writev() leaving the wrapped classic Writable
corked when conversion of a later chunk throws.

Previously, writev() called writable.cork() before converting all
chunks. If toUint8Array() threw, for example with
writer.writev([new Uint8Array([1]), 42]), execution skipped
writable.uncork() and left writable.writableCorked === 1.

This wraps the corked batch write in try/finally so the internal cork
is always released, and adds a regression test for the invalid later
chunk case.

Fixes: #63294

---

Assisted-by: openai:gpt-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.05%. Comparing base (c24e552) to head (33ae124).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/classic.js	90.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63295      +/-   ##
==========================================
- Coverage   90.05%   90.05%   -0.01%     
==========================================
  Files         714      714              
  Lines      225247   225261      +14     
  Branches    42578    42578              
==========================================
+ Hits       202842   202852      +10     
- Misses      14181    14187       +6     
+ Partials     8224     8222       -2     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/classic.js	89.17% <90.00%> (-0.18%)	⬇️

... and 30 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/73434/