stream: serialize concurrent share consumer reads

[trivikr]

This updates stream/iter share() consumers to serialize overlapping
next() calls from the same async iterator, preserving call order when
multiple reads are started before earlier reads resolve.

A regression test was added for the reported case where two concurrent
next() calls returned second before first.

Fixes: #63477

---

Assisted-by: openai:gpt-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

❌ Patch coverage is 89.65517% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.08%. Comparing base (d92ee51) to head (853f1a1).
⚠️ Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/share.js	89.65%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63478      +/-   ##
==========================================
+ Coverage   90.07%   90.08%   +0.01%     
==========================================
  Files         714      714              
  Lines      225944   225955      +11     
  Branches    42735    42742       +7     
==========================================
+ Hits       203520   203560      +40     
+ Misses      14205    14185      -20     
+ Partials     8219     8210       -9     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/share.js	84.35% <89.65%> (+0.23%)	⬆️

... and 28 files with indirect coverage changes

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