feat: abort named child runs when the parent is gracefully aborted

[vdusek]

Adds abort_with_parent to Actor.start, Actor.call, Actor.start_task and Actor.call_task. It's off by default and needs run_name. The flag is stored as abortWithParent in the name's record under __ACTOR_CHILD_RUNS, so a parent that migrated or was resurrected still knows which children to abort. The latest call under a name sets the value.

The SDK registers its own ABORTING listener on ApifyEventManager when the Actor context starts. It's kept apart from user listeners, so off() without a listener doesn't remove it. On a graceful abort, it gracefully aborts every flagged child that's still READY or RUNNING, all in parallel. If one abort fails, the error is logged and the others go ahead. Each child is aborted with the client it was started with in this process, which matters when a custom token was passed. A child from before a migration uses the default client.

A hard abort, a timeout or an OOM kill still leaves the children running. Covering that needs a parent/child link on the platform.

Closes: #1128

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.29%. Comparing base (d382995) to head (c1f6b59).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1153      +/-   ##
==========================================
+ Coverage   93.20%   93.29%   +0.09%     
==========================================
  Files          54       54              
  Lines        3721     3776      +55     
==========================================
+ Hits         3468     3523      +55     
  Misses        253      253              

Flag	Coverage Δ
e2e	32.78% <22.80%> (-0.17%)	⬇️
integration	52.33% <28.07%> (-0.38%)	⬇️
unit	90.12% <100.00%> (+0.14%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.