Implement Streams API: pipeTo, pipeThrough, tee, and byte streams (BYOB) #183

Goal#

Extend the Streams API foundation with pipe operations and the byte-oriented variants needed to model network and binary I/O.

Depends on: "Implement Streams API foundation".

Pipe operations on ReadableStream
- pipeTo(destination, options?) where options is { preventClose, preventAbort, preventCancel, signal }
- pipeThrough({ readable, writable }, options?)
- AbortSignal integration — aborting the signal aborts the pipe in both directions
- Backpressure: do not pull until the destination's writer ready resolves
- Error propagation: errors on either side propagate based on preventClose / preventAbort / preventCancel
tee() on ReadableStream
- Returns a two-element array of branches sharing one underlying source
- Both branches see the same chunks; closing/erroring is independent unless both cancel
Byte streams
- new ReadableStream({ type: 'bytes', ... })
- ReadableByteStreamController: enqueue(chunk: Uint8Array), close, error, desiredSize, byobRequest
- ReadableStreamBYOBReader: getReader({ mode: 'byob' }), read(view) → Promise<{ value: Uint8Array, done }>, releaseLock, cancel
- ReadableStreamBYOBRequest: view, respond(bytesWritten), respondWithNewView(view)
- Auto-allocate path when constructor specifies autoAllocateChunkSize
Pull-throttling: byte stream controllers only call pull while there is demand from a default reader (queued requests) or a BYOB reader (pending view requests)

readable.pipeTo(writable) resolves when the source closes and the sink finishes draining, rejecting on either side's error
readable.pipeThrough(transformStream) returns the transform's readable side and propagates errors
Aborting an AbortSignal passed to pipeTo cancels the source and aborts the sink (subject to preventCancel / preventAbort)
tee() branches independently consume the same data; cancelling both branches cancels the source
BYOB reader returns Uint8Array views with byteOffset/byteLength matching the bytes filled by the underlying source
Auto-allocate streams synthesize views of the configured size for the controller to fill
Unit tests covering pipe error propagation in all 4 prevent-flag combinations, tee correctness with backpressure, BYOB read with both auto-allocate and consumer-provided views
Conventions
- cargo fmt --all --check
- cargo clippy --workspace -- -D warnings
- cargo test --workspace