Moves the hardware-change debounce/coalescing worker (the dirty/queued flags
and re-queue logic) into a dedicated class with an injectable delay, so the
concurrency behavior can be unit-tested deterministically instead of living as
an untestable fire-and-forget block in the service. Behavior is unchanged.
Adds 3 tests (single rebuild after delay, burst coalesced to one, no rebuild
when closed) driven by a controllable delay gate.
199 tests pass (was 196).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
