New Trove update

[PhilSA]

Here's a new major Trove update, after a long hiatus:

• Packages are now on OpenUPM, for proper dependency management.
• New Trove Event Systems.
• New Trove State Machines.
• Total rewrite of Trove Stats (previously "Trove Attributes")
• Total rewrite of Trove Polymorphic Structs.

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Stats:
Previously named "Trove Attributes". The new version is much simpler, performs better, involves less boilerplate, and has more versatility.
https://github.com/PhilSA/Trove/blob/main/com.trove.stats/README.md

Event Systems:
Allows easy event creation, either as "global" events (live in a global native collection) or as "entity" events (live in a dynamicBuffer on a target entity). Supports parallel event creation, parallel read, and multiple consumers. Optionally combine with Polymorphic Structs for polymorphic ordered events. Writing variable-sized events to byte buffers is also supported via the new Polymorphic Structs.
https://github.com/PhilSA/Trove/blob/main/com.trove.eventsystems/README.md

State Machines:
Efficient, versatile state machines that can easily be made to be hierarchical/nested. Supports OnStateEnter/OnStateExit logic, can have multiple different updates for multiple different points in the frame, states that update other states, non-instant state transitions, etc... You can even use them to implement DOTS coroutines.
https://github.com/PhilSA/Trove/blob/main/com.trove.statemachines/README.md

Polymorphic Structs:
Now gives you 3 different ways to do polymorphism: Union Structs, Merged Fields Structs, and object byte writer/reader. Each have their use. Source generators were rewritten to be incremental and attributes-based, for better efficiency.
https://github.com/PhilSA/Trove/blob/main/com.trove.polymorphicstructs/README.md