stream: handle falsy push writer fail reasons

[trivikr]

This fixes stream/iter push writer reads after writer.fail() is called
with an explicit falsy reason.

Reads now use the writer state instead of the truthiness of the stored error,
so reasons like 0 and false reject correctly instead of leaving reads
pending.

Fixes: #63568

---

Assisted-by: openai:gpt-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.33%. Comparing base (8b88e2c) to head (bdda946).

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/push.js	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63569      +/-   ##
==========================================
- Coverage   91.95%   90.33%   -1.63%     
==========================================
  Files         379      732     +353     
  Lines      166486   236459   +69973     
  Branches    25452    44534   +19082     
==========================================
+ Hits       153099   213610   +60511     
- Misses      13094    14548    +1454     
- Partials      293     8301    +8008     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/push.js	91.63% <90.00%> (+0.05%)	⬆️

... and 478 files with indirect coverage changes

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[mcollina]

lgtm