Test Allocations

[lukem12345]

For some physics in which we expect there to be 0 allocations, we should explicitly and programmatically test that there are no allocations.

A simple test is that of the heat equation written with 2 Vars and 2 Op1s.

For some physics in which we expect there to be nonzero allocations, we should ... test that the expected number/ size of allocations occurs.

Further, it would be nice to check whether the performance in the latter case can be improved if we provide a heuristically-derived value to be passed to sizehint.