fix: prune invalid/freed keys before typed-array assignments

[gk98s]

Rather than modifying the synchronisers' core reparenting-preservation logic, this PR introduces a self-healing defensive prune inside Netfox's central data containers.

Before keys are fetched, assigned to typed arrays, or passed to prediction checks, the internal dictionaries are scanned for freed references via is_instance_valid(). Any dead references are safely erased from the dictionary before any typed array assignment takes place.

Fixes #621

[elementbound]

I'll look into the issue, but I'd much prefer not to filter the whole list on each query. My fear is that this could cause significant slowdowns.

[gk98s]

Fair enough, I was too focused on fixing the errors I didn't notice the performance impact. I've just made an alternative fix that should be way better performance wise, and still fixes the crash and the errors I was having.