Fix problems with heaps larger than 512 and other fixes

This release enforces that all custom behaviours inherit from UdonSharpBehaviour and not MonoBehaviour if you have any classes that break, you will likely need to make them inherit from UdonSharpBehaviour to be compliant with this.

• a35a6bd: Allow the heap to resize to fit the number of heap values that get used by the program instead of just using a fixed size of 512. This will expand up to an internal limit of 16384 heap values so it should be good enough for now. More effective reuse of heap variables is a target for improvement.
• 69b2d12: Add handling for implicitly converting operators to higher precision operators in cases where you are adding two types like adding int and uint which will output a long in the C# compiler. Reported by @Foorack
• a6ec5df: Enforce that custom behaviours inherit from UdonSharpBehaviour for now since it can cause issues that aren't clear to debug when you don't inherit from them. Reported by @cubedparadox