More streams test consolidation and gap filling

[jasnell]

No description provided.

[ask-bonk]

Promise.all() starts the fetches but does not require their handlers to overlap: these streams were already filled and closed during module evaluation, so serial request handling produces the same response text. Gate the handlers until all four requests have arrived, so a regression that serializes this path cannot pass the test.

Suggested change

	if (url.pathname.startsWith('/pool/')) {
	if (url.pathname.startsWith('/pool/')) {
	const i = Number(url.pathname.split('/')[2]);
	const state = (globalThis.poolRequestBarrier ??= (() => {
	let release;
	return {
	entered: 0,
	wait: new Promise((resolve) => {
	release = resolve;
	}),
	release: () => release(),
	};
	})());
	if (++state.entered === streamPool.length) state.release();
	await state.wait;
	return new Response(streamPool[i]);
	}

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

Adds stream transfer/clone, IoContext concurrency, piping, and writable queue-accounting coverage.

1. P2 src/tests/streams/iocontext/global-scope-streams.js:384: The concurrency test permits serialized request handling. Posted one inline suggestion to gate all four handlers.

Time for a pun! That concurrency test needs a little more stream team.

github run