stream: add fast paths for webstreams read and pipeTo

[mcollina]

Add internal fast paths to improve webstreams performance without changing the public API or breaking spec compliance.

1. ReadableStreamDefaultReader.read() fast path: When data is already buffered in the controller's queue, return PromiseResolve() directly without creating a DefaultReadRequest object. This is spec-compliant because read() returns a Promise, and resolved promises still run callbacks in the microtask queue.

2. pipeTo() batch read fast path: When data is buffered, batch reads directly from the controller queue up to highWaterMark without creating PipeToReadableStreamReadRequest objects per chunk. Respects backpressure by checking desiredSize after each write.

Benchmark results:

• pipeTo: ~11% faster (***)
• buffered read(): ~17-20% faster (***)

This was done in partnership with Vercel to improve the performance of React and Next.js, and from a conversation on X with @cramforce.

[nodejs-github-bot]

Review requested:

• @nodejs/performance
• @nodejs/web-standards

[codecov]

Codecov Report

❌ Patch coverage is 97.59036% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.76%. Comparing base (ae2ffce) to head (5e0474e).
⚠️ Report is 70 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	97.59%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61807      +/-   ##
==========================================
+ Coverage   89.75%   89.76%   +0.01%     
==========================================
  Files         674      675       +1     
  Lines      204416   204818     +402     
  Branches    39285    39359      +74     
==========================================
+ Hits       183472   183859     +387     
- Misses      13227    13233       +6     
- Partials     7717     7726       +9     

Files with missing lines	Coverage Δ
lib/internal/webstreams/readablestream.js	98.42% <97.59%> (-0.03%)	⬇️

... and 64 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71335/