stream: settle pending broadcast reads on return

[trivikr]

This updates broadcast async iterator cleanup so a pending
next() settles when the consumer is returned.

When a broadcast consumer has an outstanding next() and
return() is called before data arrives, the pending read is now
resolved with { done: true, value: undefined } during detach.

Fixes: #63519

---

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 90.31%. Comparing base (4639dcb) to head (273ae63).
⚠️ Report is 28 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #63603 +/- ##
==========================================
+ Coverage 90.29% 90.31% +0.02% 
==========================================
Files 730 730 Lines 234695 234696 +1 Branches 43956 43954 -2 ==========================================
+ Hits 211927 211976 +49 + Misses 14494 14431 -63 - Partials 8274 8289 +15 

Files with missing lines	Coverage Δ
lib/internal/streams/iter/broadcast.js	85.25% <100.00%> (+0.01%)	⬆️

... and 48 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/73817/

[mcollina]

lgtm

[nodejs-github-bot]

Landed in 040c51c