Adding `compile_function` as execute option.

[alxmrs]

This allows users to use jit or aot compilation during the dag finalization process within executors. It should work straightforwardly on jax/numba style jit compilation. It's possible, but maybe ugly, to perform jax-aot-style compilation.

This should help make progress towards #304.

(Note to reviewer: I realized this could be merged ahead of #508, so I pulled it out into a non-dependent PR).