feat: add max_total_charge_usd to task start() and call()

[vdusek]

TaskClient.start() and call(), sync and async, now accept max_total_charge_usd and send it as the maxTotalChargeUsd query parameter, matching ActorClient and the JS client's task.start().

The SDK needs this for apify/apify-sdk-python#1155 so that named task child runs can share the parent's charge budget.

Closes: #1096

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.35%. Comparing base (3dd8ca5) to head (ef817a1).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1097   +/-   ##
=======================================
  Coverage   95.35%   95.35%           
=======================================
  Files          61       61           
  Lines        5808     5808           
=======================================
  Hits         5538     5538           
  Misses        270      270           

Flag	Coverage Δ
integration	90.92% <ø> (-0.09%)	⬇️
unit	88.13% <ø> (ø)

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[Mantisus]

LGTM

[apify-approval-mirror]

Mirroring approval from @Mantisus.