test: fix flaky test_request_queue_unlock_requests

[vdusek]

Summary

Fix this flaky CI run of test_request_queue_unlock_requests[sync], which failed with assert 2 == 3 on unlock_response.unlocked_count.

Root cause: server-side replication lag. list_and_lock_head(limit=3) acknowledges 3 locks on one replica, but the immediately following unlock_requests() reads a replica where only 2 of the 3 lock writes had propagated, so it reports unlocking 2. The [async] variant passed in the same run — only [sync] lost the race, which is characteristic of a flake rather than a regression.

Fix: wait for the locks to propagate before unlocking, using a poll_until_condition helper instead of a fixed sleep. Locked requests are excluded from the queue head, so the test polls list_head until none of the just-locked request IDs reappear there — i.e. all three lock writes have become visible to subsequent reads. (get_request exposes no lock field, so it can't be used as the signal.)

This is a follow-up to #786, which removed the earlier cross-iteration locking ambiguity; this addresses the remaining lock→unlock replication race.

Commits

1. Add the poll_until_condition / call_with_exp_backoff test helpers (shared signatures with apify-sdk-python / crawlee-python) and rebuild collect_iterate_until_present on top of poll_until_condition.
2. Use poll_until_condition to fix the flaky test_request_queue_unlock_requests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.74%. Comparing base (beab127) to head (ad43eec).

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #844       +/-   ##
===========================================
+ Coverage   83.52%   94.74%   +11.21%     
===========================================
  Files          48       48               
  Lines        5045     5045               
===========================================
+ Hits         4214     4780      +566     
+ Misses        831      265      -566     

Flag	Coverage Δ
integration	93.14% <ø> (?)
unit	83.52% <ø> (ø)

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