fix: preserve original expiration window on stale claim reclaim #13

DS-Review completed

PR: fix: preserve original expiration window on stale claim reclaim

Important

Verdict: Request changes — tests must assert that expires_at is preserved after reclaim to prevent regression.

Pri	Location	Finding	Action
`P2`	`tests/test_store.py:325`	Missing assertion that `expires_at` is preserved after reclaim	Add assertion comparing commit's `expires_at` to original value
`P2`	`tests/test_async_client.py:312`	Missing assertion that `expires_at` is unchanged and cache hit works	Add `expires_at` assertion and second submission to confirm cache hit
`P3`	`tests/test_async_client.py:282`	Test name includes "with_ttl" but no TTL is set	Rename test to reflect actual scenario

Both new tests validate that stale claims are reclaimed and function re-executes, but neither checks that the original expires_at is preserved. Without these assertions, a regression that recalculates expires_at would not be caught.
The async test also does not verify that a subsequent submission returns from cache without re-execution.

Add assertions for expires_at in both test_reclaimed_stale_claim_keeps_original_expires_at and test_cached_task_with_ttl_and_stale_reclaim.
In the async test, add a second submit call to confirm the cache hit (counter should not increment).