stream: fix unhandled rejection for errored pipeTo writes

[dushyant-hada-90]

Fixes a v26.4.0 regression where ReadableStream.pipeTo() could crash the
process with an unhandled rejection even when the pipeTo() promise
rejection was already caught.

In #63572, per-chunk setPromiseHandled() was replaced with
markPromiseAsHandled(). That is safe for pending write promises, but when
a later chunk is written after the destination has already errored,
writableStreamDefaultWriterWrite() returns an already-rejected promise.
Marking that promise handled afterwards does not cancel V8's pending
unhandled-rejection notification.

This keeps markPromiseAsHandled() on the writable fast path and falls
back to setPromiseHandled() when the destination is no longer writable
(or close is queued/in flight).

No documentation changes; behavior is restored to match Node.js ≤ v26.3.1,
Deno, Bun, and browsers.

Checklist

• make -j4 test (UNIX) or vcbuild test (Windows) passes / CI will validate
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Fixes: #64561
Refs: #63572

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.24%. Comparing base (fb5d01f) to head (3cfa60c).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64580      +/-   ##
==========================================
- Coverage   90.24%   90.24%   -0.01%     
==========================================
  Files         739      739              
  Lines      241772   241787      +15     
  Branches    45561    45571      +10     
==========================================
- Hits       218194   218192       -2     
- Misses      15111    15120       +9     
- Partials     8467     8475       +8     

Files with missing lines	Coverage Δ
lib/internal/webstreams/readablestream.js	98.19% <100.00%> (+<0.01%)	⬆️

... and 30 files with indirect coverage changes

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