feat: Expose missing platform env vars via Actor.get_env()

[vdusek]

Part of the v4 major-release cleanup.

Configuration already reads ACTOR_STORAGES_JSON, ACTOR_TEST_PAY_PER_EVENT, APIFY_ACTOR_PRICING_INFO, and APIFY_CHARGED_ACTOR_EVENT_COUNTS, but Actor.get_env() silently omitted them because the matching members were missing from the vendored ActorEnvVars / ApifyEnvVars enums. This adds the four members so get_env() surfaces them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.95%. Comparing base (0daca28) to head (321fdea).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #984      +/-   ##
==========================================
+ Coverage   89.90%   89.95%   +0.04%     
==========================================
  Files          49       49              
  Lines        3091     3095       +4     
==========================================
+ Hits         2779     2784       +5     
+ Misses        312      311       -1     

Flag	Coverage Δ
e2e	35.99% <100.00%> (+0.08%)	⬆️
integration	56.96% <100.00%> (+0.08%)	⬆️
unit	78.77% <100.00%> (+0.02%)	⬆️

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