fix: Ensure transport connection events don't act if duplicated

[EmandM]

Purpose of this PR

Ensures duplicate events are ignored if the transport layer:

1. Sends the server multiple connection events for the same client
2. Sends a client multiple connection events from the server

Jira ticket

UUM-131553)

Changelog

• Fixed: Duplicate connection events for the same connection will do nothing.

Documentation

• No documentation changes or additions were necessary.

Testing & QA (How your changes can be verified during release Playtest)

Functional Testing

Manual testing :

• Manual testing done

Automated tests:

• Covered by existing automated tests
• Covered by new automated tests

Does the change require QA team to:

• Review automated tests?
• Execute manual tests?
• Provide feedback about the PR?

If any boxes above are checked the QA team will be automatically added as a PR reviewer.

Backports

No backport needed

[michalChrobot]

We are not modifying UnityTransport folder here but maybe it's still worth it to request review from Simon?