🐛 Enforcing the waitForGeneration timeout on in-flight polls and retries

[simonc]

waitForGeneration documents timeout as a total budget, but it was only checked between polls. A slow get() (and its internal retries) could run past it: a late success resolved, and a late pending response only reported the timeout once it came back.

Changes

• The budget is now a deadline AbortController, composed with the caller's signal and passed to every poll and to the sleep between polls. When it fires, the in-flight request is aborted and the call rejects with the usual "timed out" error.
• Caller cancellation still surfaces as an abort, not a timeout; a pre-aborted signal still rejects without polling.
• Regression tests with a slow, abort-aware fetch (late success, late pending, caller abort, pre-aborted signal). The first two fail without the fix.
• Patch changeset.