stream: serialize concurrent share consumer reads

[trivikr]

This updates stream/itershare() 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 81.35593% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.13%. Comparing base (8d3245e) to head (1d297dc).
⚠️ Report is 72 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/share.js	81.35%	10 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #63478 +/- ##
==========================================
- Coverage 90.14% 90.13% -0.01% 
==========================================
Files 718 718 Lines 227984 227995 +11 Branches 42835 42829 -6 ==========================================
- Hits 205522 205513 -9 - Misses 14235 14253 +18 - Partials 8227 8229 +2 

Files with missing lines	Coverage Δ
lib/internal/streams/iter/share.js	84.19% <81.35%> (-1.66%)	⬇️

... and 29 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/73753/

[nodejs-github-bot]

Landed in 5174c66