fix: allow max_retries=0 to disable retries

[vdusek]

max_retries counts retries, so 0 should mean a single attempt. Instead, every request with max_retries=0 raised ValueError from the retry loop. Now 0 disables retries, and a negative value raises ValueError when ApifyClient, ApifyClientAsync or an HTTP client is constructed.

This is a regression from 3.0.0. Up to 2.5.1, max_retries=0 made exactly one attempt; the ValueError check came in with #604. The JS client also accepts 0.

The tests in test_client_errors.py that meant to avoid retries used max_retries=1, which still retries once. They now use 0.

Closes: #1139

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.50%. Comparing base (53a9954) to head (7f1153a).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1142      +/-   ##
==========================================
+ Coverage   95.43%   95.50%   +0.06%     
==========================================
  Files          61       61              
  Lines        5935     5937       +2     
==========================================
+ Hits         5664     5670       +6     
+ Misses        271      267       -4     

Flag	Coverage Δ
integration	90.76% <50.00%> (-0.04%)	⬇️
unit	88.91% <100.00%> (+0.03%)	⬆️

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