Cleanup Unused Channels in RealtimeMixin

What does this PR do?

This pull request addresses the issue of concurrent modification errors in the RealtimeMixin class. Specifically, it modifies the _createSocket and _cleanup methods to avoid modifying collections while iterating over them. This resolves the concurrent modification errors encountered during iteration

Test Plan

I tested these changes by running the application and observing that the concurrent modification errors no longer occur. The specific test plan involved:

1. Subscribing to multiple real-time channels.
2. Triggering events to ensure subscriptions work as expected.
3. Cleaning up unused channels and ensuring no concurrent modification errors are thrown.

Related PRs and Issues

This pull request resolves the following issues:

🐛 Bug Report: RealTime subscribe throws Concurrent modification during iteration: _Map len:0#200
🐛 Bug Report: Concurrent Modification Error in RealtimeMixin Causing Crashes#203

Have you read theContributing Guidelines on issues?

Yes