Makes CollectionStorage thread safe for parallel initialization of collections by one or multiple IPC consumers without requring framework thread synchronization.

[Mayo66]

Summary

As of now, most collection operations require being called on the framework thread despite not needing access to game objects.

However, It is only when assigning via AssignTemporaryCollection(), in which it accesses (ObjectManager)objects[actorIndex] when framework thread is needed.

By making the internal data structures thread-safe, we can move collection management operations off the framework thread when safe and in doing so avoiding framework thread bottlenecks and reduce hitches, while avoiding desynchronizations between multiple consumers.

Changes

• _collectionsByLocal: Changed to ConcurrentDictionary for lock free concurrent access
• _collections: Added locking to protect concurrent modifications
• CurrentCollectionId: Implemented atomic increment
• Discovery / Change handlers: Snapshot collections before iteration to prevent concurrent modification exceptions
• Collection Addition: Extracted collection addition logic to into dedicated Add() for clarity.

This should make the following IPC methods safe for off-framework access:

• CreateTemporaryCollection()
• DeleteTemporaryCollection()

AssignTemporaryCollection() still needs framework access as it is the crucial step when a collection is associated with a game object.

Misc

There was also a duplicate operation at line 189 in the original file, method RemoveCollection():
_collectionsByLocal.Remove(collection.Identity.LocalId);
at line 183 in the original file, Delete(collection); is called, which is simply

public void Delete(ModCollection collection)
        => _collectionsByLocal.Remove(collection.Identity.LocalId);

The call at line 189 looks like a duplicate, and this PR also removes said duplicate operation.

[Mayo66]

now increments upon generating a new id to avoid scenarios when two threads call an CreateFrom method at the same time and one overwriting the other

[Mayo66]

added locking to public methods