stream: validate writer options signal

[trivikr]

Fixes: #64384

stream/iterwriter methods now validateoptions.signal` consistently
before using or ignoring it.

This updates push, broadcast, and fromWritable writer write(),
writev(), and end() so invalid options.signal values throw
ERR_INVALID_ARG_TYPE instead of causing inconsistent behavior.

---

Assisted-by: openai:gpt-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.25%. Comparing base (0032189) to head (a56cebf).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64385      +/-   ##
==========================================
+ Coverage   90.23%   90.25%   +0.02%     
==========================================
  Files         741      741              
  Lines      241194   241220      +26     
  Branches    45432    45424       -8     
==========================================
+ Hits       217640   217712      +72     
+ Misses      15129    15073      -56     
- Partials     8425     8435      +10     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/broadcast.js	85.99% <100.00%> (+0.03%)	⬆️
lib/internal/streams/iter/classic.js	89.32% <100.00%> (+0.06%)	⬆️
lib/internal/streams/iter/push.js	91.17% <100.00%> (+0.32%)	⬆️
lib/internal/streams/iter/utils.js	98.26% <100.00%> (+0.06%)	⬆️

... and 28 files with indirect coverage changes

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