[Reset] Handle completion events from restarted children

[gow]

What changed?

In this PR we are doing 2 things,

1. Cleaning up the entries in ChildrenInitializedPostResetPoint
2. Verifying that the results are indeed from the correct restarted child before accepting the completion event.

Why?

• Cleans up the mutable state and reduces bloat.
• Avoids a race condition where a old child completed in between the time when new child Init is recorded and when it is actually started.

How did you test it?

Added unit tests + manual testing.

Potential risks

N/A

Documentation

Pending

Is hotfix candidate?

No

[github-actions[bot]]

This PR was marked as stale. Please update or close it.