Cache bytecode compilations

[cameronfyfe]

Cache the segment proof for bytecode compilation.

Investigate best method. Two possible methods:

1. Use continuations to pause between "py code -> bytecode" compilation and running the bytecode
2. Use composition to combine a "py code -> bytecode" proof and a "run bytecode" proof.

In either case, a caching mechanism managed by the host to recognize when proofs for the same python script can be re-used needs to be added. This could be done just locally, or with support for querying external sources for cached segment proofs.