feat: overcharge by one event when the PPE budget is exhausted

[vdusek]

When a charge goes over the remaining max_total_charge_usd budget, the SDK charges one event more than the budget covers, so the platform detects the exhausted budget and stops the run. push_data lets one item through when the budget can't cover a single one, and a run that is already strictly over budget gets nothing more. This ports the JS SDK behavior from apify/apify-sdk-js#574. As in JS, the push data limit applies only to pay-per-event runs.

It changes what users see: a run sitting exactly at its budget gets one more event on the next charge, max_total_charge_usd=0 lets one event through, and callers that ignore ChargeResult can get one extra charged event and dataset item. The charge() docstrings and the exceptions docs page describe the rule.

The PPE E2E tests are updated for the new counts. test_actor_charge_limit expects 3 charges, as the JS E2E test does. The Scrapy PPE spider test uses a $0.075 budget, expects 2 charges and 2 items, and accepts SUCCEEDED or ABORTED, since the platform's abort can race the Actor's own exit.

Closes: #1187

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.10%. Comparing base (290af90) to head (9fbb5db).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1191      +/-   ##
==========================================
+ Coverage   93.00%   93.10%   +0.10%     
==========================================
  Files          54       54              
  Lines        3672     3683      +11     
==========================================
+ Hits         3415     3429      +14     
+ Misses        257      254       -3     

Flag	Coverage Δ
e2e	31.65% <6.25%> (-0.07%)	⬇️
integration	51.56% <6.25%> (-0.13%)	⬇️
unit	89.84% <100.00%> (+0.11%)	⬆️

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