fix: prevent silent loss of reclaimed requests during queue head propagation

[vdusek]

A request reclaimed with the default forefront=False (crawlee's BasicCrawler retry path) was written only to _requests_cache, which is_empty() and is_finished() never consult — they read the local head estimate. With the request in no head structure, both reported the queue finished while the platform head listing still lagged behind the reclaim. Near queue exhaustion, AutoscaledPool polls is_finished(), gets True from the lagging head, and shuts the run down: the request stays pending in the queue forever while the run reports success.

The fix re-enters the reclaimed id at the back of the local head estimate (_head_requests.appendleft for the single client, _queue_head.append for the shared client), mirroring add_batch_of_requests and the existing forefront=True branch, so the request is retried instead of dropped. The forefront=True paths are unchanged.

Regression tests for both clients reclaim a request while the mocked platform head lags and assert is_empty()/is_finished() stay False — they fail before the fix.

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.00%. Comparing base (58d6da1) to head (0136f4a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1060      +/-   ##
==========================================
+ Coverage   91.89%   92.00%   +0.10%     
==========================================
  Files          51       51              
  Lines        3232     3238       +6     
==========================================
+ Hits         2970     2979       +9     
+ Misses        262      259       -3     

Flag	Coverage Δ
e2e	?
integration	57.16% <100.00%> (+0.07%)	⬆️
unit	85.79% <100.00%> (+2.53%)	⬆️

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