stream: speed up WHATWG web streams

[anonrig]

Behavior-preserving performance work on node:stream/web. Spec
orchestration and brand checks stay in JS; the per-chunk data plane
drops Promise/microtask churn for the common sync pull/write case
and gets a small native helper on the hot path.

• Skip async wrappers on sync source/sink algorithms.
  createPromiseCallback* now calls the user function and returns
  the raw result. Non-thenable results settle via queueMicrotask
  (same position as Promise.resolve().then) instead of allocating
  a Promise per pull/write/start.
• pipeTo fills a default readable queue from sync pulls and
  still batches already-queued chunks into the destination. Further
  spec pull-fulfillment (tee, WPT) stays one pull per microtask.
• pipeTo's shared write tracker completes sync sink writes in
  the fulfillment turn. Regular writer.write() keeps the spec
  one-completion-per-microtask order.
• Native internalBinding('webstreams'): Fast API
  isNonThenable() on every pull/write/start result, and
  cloneAsUint8Array() as a single memcpy for byte-stream / tee
  clones.
• Cheaper empty construction. new ReadableStream() /
  new WritableStream() skip validateObject on the shared empty
  sentinels. The writable AbortController is created lazily and
  materialized on abort(), so controller.signal observed after
  abort is still aborted with that reason.

Public constructors, methods, and WHATWG Streams behavior
(backpressure, BYOB, pipeTo, tee, errors, transfer) are unchanged.

Benchmarks

benchmark/compare.js --runs 10 of the in-repo webstreams/ suite
on the same machine, same out/Release/node family (pre-change
binary vs this tree). Rates are ops/sec.

Hot-path geometric mean of new/old across all configs of
pipe-to.js, readable-read.js, readable-read-buffered.js,
creation.js, readable-async-iterator.js, and tee.js:
1.94x (32 configs). Full suite including js_transfer.js:
1.84x (35 configs). No config has mean(new)/mean(old) < 1.0
(min 1.03 on js_transfer ReadableStream).

script	config	old	new	ratio
pipe-to	HWM 512/512	2.15M	4.83M	2.25
pipe-to	HWM 4096/4096	2.17M	4.85M	2.24
tee	normal	1.12M	2.56M	2.29
readable-async-iterator	normal	3.77M	8.59M	2.28
creation	WritableStream	0.67M	1.37M	2.05
readable-read-buffered	bufferSize=1000	5.61M	12.17M	2.17
readable-read	normal	3.99M	5.37M	1.35
creation	ReadableStream	1.35M	2.01M	1.49
js_transfer	ReadableStream	59.0k	61.0k	1.03

Tests

• test/wpt/test-streams.js
• test/parallel/test-whatwg-readable*, writable*, transform*,
  webstreams*, test-webstreams*, test-global-webstreams.js
• new test/parallel/test-whatwg-webstreams-hotpath.js (public
  read() / pipeTo, native helpers, abort-before-signal)
• abort-before-signal case in test-whatwg-writablestream.js

AI assistance

This change was developed with assistance from Grok. I reviewed,
tested, and take responsibility for the submitted code.

[nodejs-github-bot]

Review requested:

• @nodejs/gyp

[codecov]

Codecov Report

❌ Patch coverage is 94.54545% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.32%. Comparing base (e1cdcec) to head (8ce1778).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_webstreams.cc	78.26%	6 Missing and 4 partials ⚠️
lib/internal/webstreams/readablestream.js	93.75%	7 Missing ⚠️
lib/internal/webstreams/writablestream.js	98.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65273      +/-   ##
==========================================
+ Coverage   90.31%   90.32%   +0.01%     
==========================================
  Files         751      752       +1     
  Lines      249840   250266     +426     
  Branches    47180    47282     +102     
==========================================
+ Hits       225645   226064     +419     
- Misses      15587    15591       +4     
- Partials     8608     8611       +3     

Files with missing lines	Coverage Δ
lib/internal/webstreams/transformstream.js	98.58% <100.00%> (+0.01%)	⬆️
lib/internal/webstreams/util.js	97.89% <100.00%> (+0.17%)	⬆️
src/node_binding.cc	82.42% <ø> (ø)
src/node_external_reference.h	100.00% <ø> (ø)
lib/internal/webstreams/writablestream.js	99.47% <98.88%> (-0.05%)	⬇️
lib/internal/webstreams/readablestream.js	98.03% <93.75%> (-0.14%)	⬇️
src/node_webstreams.cc	78.26% <78.26%> (ø)

... and 47 files with indirect coverage changes

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[jasnell]

Defensively marking this semver-major. If you can show that the optimization does not change observable behavior, that can be dropped, but the change in microtask timing from one pull to the next is likely observable.

[anonrig]

@jasnell I believe semver-major is no longer needed.

[github-actions]

Benchmark GHA (webstreams): https://github.com/nodejs/node/actions/runs/31808780686