When invoking UdonHeap.SetHeapVariable, in UdonHeap.SetHeapVariableInternal, a new StrongBox is constructed unconditionally, even if the StrongBox in the heap already has the correct type. This results in GC pressure whenever a cross-UdonBehaviour heap variable is set (which occurs whenever we perform a U# method call with parameters across behaviours).
This could be resolved by reusing the StrongBox, as in CopyHeapVariable.