settled() awaits renderSettled() instead of polling the render half - #2214

The @ember/test-helpers patch restructures settled(): the render
condition is event-driven (await renderSettled(), which resolves at the
end of a scheduler flush that left every renderer valid) and only the
poll-only conditions (test waiters, pending requests, transitions)
re-check in a loop.

Quiet is confirmed from a macrotask before resolving: already-queued
task sources (worker messages, zero-delay timers) may re-register
waiters or dirty state, and a microtask-context observation wins the
race against them and settles early -- observed as a real 1-in-4 flake
in ember-repl's Compiled() tests until the setTimeout confirm was
added. waitUntil imposed the same boundary implicitly by scheduling
every check via setTimeout.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

The tarball moves to all-optimizations+c09efdc8, which replaces the
isRenderPending() probe with edge reporting: the renderer notifies when
work becomes outstanding and when it completes. The @ember/test-helpers
patch turns those edges into an @ember/test-waiters waiter, so
rendering settles through the same protocol as every other async
source -- isSettled() needs no render clause (its old one is hardwired
false to avoid double-counting), and a stuck render is named in
test-waiter debug output.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Reworks the settledness patches per review on
emberjs/ember-test-helpers#1574: @ember/test-waiters creates a promise
per operation in beginAsync, endAsync resolves it and drops it from the
pending map, and waitersSettled() composes the promises of whatever is
still in flight. @ember/test-helpers' settled() awaits that alongside
renderSettled().

The fallback tick stays for waiters that cannot announce completion
(pull-only Waiter implementations -- waitersSettled returns a
never-resolving promise while one is pending -- plus legacy waiters and
request counters). It is 50ms rather than 10 so it loses the race to a
frame-paced render tick; at 10ms it decided 30 of 117 iterations.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>