fix: cap _list_head request limit at _MAX_HEAD_ITEMS

[vdusek]

Summary

ApifyRequestQueueSingleClient._list_head used max instead of min when computing the limit passed to the Apify API:

requested_head_items = max(self._MAX_HEAD_ITEMS, desired_new_head_items + len(self._requests_in_progress))

Two problems with this:

1. Over-fetch in the common case. When desired + in_progress < 1000, max forces the limit to 1000, pulling up to 5× more items than the logic actually wants (e.g. 1000 instead of 200 on a fresh queue).
2. API cap breach when the queue is busy. When len(self._requests_in_progress) > 800, the sum exceeds _MAX_HEAD_ITEMS = 1000 and max picks that larger value as the limit, violating the documented API cap.

The comment on the preceding line describes the intended "pad, then cap" behavior — the code should pad by in-progress count and then cap at the API maximum. Fix is one character: max → min.

Added three parametrized regression cases covering no-in-progress, mid-queue padding, and the cap boundary.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.67%. Comparing base (16bf07d) to head (55d478a).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #869      +/-   ##
==========================================
+ Coverage   86.64%   86.67%   +0.03%     
==========================================
  Files          48       48              
  Lines        2920     2920              
==========================================
+ Hits         2530     2531       +1     
+ Misses        390      389       -1     

Flag	Coverage Δ
e2e	37.87% <0.00%> (ø)
integration	59.31% <100.00%> (+0.03%)	⬆️
unit	75.37% <100.00%> (+0.68%)	⬆️

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