stream: avoid retrying accepted pipeTo writes

[trivikr]

pipeTo() treated writeSync() / writevSync() returning false as a
failed sync write and retried the same chunk(s) through the async path.

That is incorrect for PushWriter with backpressure: 'block', where
false means the data was accepted but the writer is now backpressured. This
caused duplicated output such as abcdcd instead of abcd, and abbb
instead of ab.

This updates pipeTo() to detect that internal writer case and wait for drain
instead of retrying accepted data. It also adds regression coverage for both
the single-chunk writeSync() path and the multi-chunk writevSync() path.

Fixes: #63296

---

Assisted-by: openai:gpt-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.05%. Comparing base (c24e552) to head (921ab42).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/pull.js	87.50%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #63297   +/-   ##
=======================================
  Coverage   90.05%   90.05%           
=======================================
  Files         714      714           
  Lines      225247   225289   +42     
  Branches    42578    42594   +16     
=======================================
+ Hits       202842   202891   +49     
+ Misses      14181    14175    -6     
+ Partials     8224     8223    -1     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/push.js	92.03% <100.00%> (+0.63%)	⬆️
lib/internal/streams/iter/types.js	100.00% <100.00%> (ø)
lib/internal/streams/iter/pull.js	85.23% <87.50%> (+0.07%)	⬆️

... and 28 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/73436/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/73440/