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 92.53472% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.07%. Comparing base (a844473) to head (540f9ec).
⚠️ Report is 3 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	87.09%	9 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	97.05%	2 Missing ⚠️
lib/internal/streams/iter/duplex.js	97.50%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #65652    +/-   ##
========================================
  Coverage   90.07%   90.07%            
========================================
  Files         754      754            
  Lines      256378   256636   +258     
  Branches    48498    48565    +67     
========================================
+ Hits       230936   231172   +236     
- Misses      16572    16580     +8     
- Partials     8870     8884    +14     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/utils.js	99.11% <100.00%> (+0.87%)	⬆️
lib/internal/streams/iter/duplex.js	97.39% <97.50%> (+1.04%)	⬆️
lib/internal/streams/iter/consumers.js	96.76% <97.05%> (+0.13%)	⬆️
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	91.28% <87.09%> (-0.20%)	⬇️
lib/internal/streams/iter/broadcast.js	88.56% <80.28%> (+0.12%)	⬆️

... and 23 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/76776/

[mcollina]

RSLGTM