test: cover PPE charging on the Scrapy integration end-to-end

[vdusek]

Adds an e2e test that runs a pay-per-event Scrapy Actor on the platform and asserts that pushed items are charged and that max_total_charge_usd is enforced. The spider scrapes three products; at $0.05 an item a $0.125 budget covers two, so the third push must be dropped and never charged.

No source changes — the behavior was already correct. This locks it in so a future Scrapy or Twisted upgrade that does change the reactor's scheduling context fails loudly instead of silently costing developers revenue.

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.37%. Comparing base (fcc767a) to head (f6a6794).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1096      +/-   ##
==========================================
+ Coverage   92.31%   92.37%   +0.06%     
==========================================
  Files          51       51              
  Lines        3317     3317              
==========================================
+ Hits         3062     3064       +2     
+ Misses        255      253       -2     

Flag	Coverage Δ
e2e	34.73% <ø> (ø)
integration	56.55% <ø> (ø)
unit	87.00% <ø> (+0.06%)	⬆️

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