stream: fix pipeToSync byte accounting

[trivikr]

Fixes: #63562

pipeToSync() ignored explicit false returns from writeSync() and
writevSync(), so it could report bytes for chunks that were not accepted by
the writer.

This updates pipeToSync() to stop counting rejected sync writes while still
preserving writers that intentionally return false after accepting data as a
backpressure signal.

---

Assisted-by: openai:gpt-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.33%. Comparing base (49dcaa0) to head (8b50431).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/pull.js	88.88%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #63564    +/-   ##
========================================
  Coverage   90.33%   90.33%            
========================================
  Files         730      730            
  Lines      234362   234487   +125     
  Branches    43906    43932    +26     
========================================
+ Hits       211713   211835   +122     
- Misses      14371    14389    +18     
+ Partials     8278     8263    -15     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/pull.js	88.09% <88.88%> (-0.03%)	⬇️

... and 43 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[trivikr]

Converted to draft as behavior should be confirmed in specification

Details #63562 (comment)