stream: apply multiple stream/iter fixes

[jasnell]

Nine commits, nine issues:

1. pull() cancellation cannot preempt a pending next()
2. transformed push, broadcast, and share consumers leak their underlying side
3. terminating a push consumer can make writer.end() hang forever
4. byte-budget accounting is derived from mutable data
5. writev() can resolve after losing the entire outer write
6. DuplexChannel close() does not close an unread incoming direction
7. merge() mishandles arbitrary errors and can block error propagation forever
8. Share cancellation cannot interrupt the pull owner
9. pipeToSync() starts asynchronous close work that nobody can observe

Recommend reviewing each commit separately.

Plus one minor cleanup commit.

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

❌ Patch coverage is 91.74147% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.05%. Comparing base (045ff95) to head (23b211e).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/broadcast.js	80.28%	14 Missing ⚠️
lib/internal/streams/iter/push.js	84.70%	10 Missing and 3 partials ⚠️
lib/internal/streams/iter/pull.js	95.15%	8 Missing ⚠️
lib/internal/streams/iter/share.js	91.78%	6 Missing ⚠️
lib/internal/streams/iter/consumers.js	93.54%	4 Missing ⚠️
lib/internal/streams/iter/duplex.js	97.14%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65652      +/-   ##
==========================================
- Coverage   91.79%   90.05%   -1.75%     
==========================================
  Files         402      754     +352     
  Lines      181164   255981   +74817     
  Branches    27776    48374   +20598     
==========================================
+ Hits       166308   230519   +64211     
- Misses      14517    16574    +2057     
- Partials      339     8888    +8549     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/utils.js	99.11% <100.00%> (+0.87%)	⬆️
lib/internal/streams/iter/duplex.js	97.27% <97.14%> (+0.92%)	⬆️
lib/internal/streams/iter/consumers.js	95.44% <93.54%> (-1.19%)	⬇️
lib/internal/streams/iter/share.js	87.38% <91.78%> (+0.96%)	⬆️
lib/internal/streams/iter/pull.js	83.96% <95.15%> (+0.61%)	⬆️
lib/internal/streams/iter/push.js	91.19% <84.70%> (-0.28%)	⬇️
lib/internal/streams/iter/broadcast.js	88.56% <80.28%> (+0.12%)	⬆️

... and 484 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/76741/