Prove Optimized Code

[sjudson]

In #138 we set opt-level = 0 for the default proving profile (release-unoptimized, as opposed to opt-level = 3 for release). This was due to the appearance of PANICs when trying to prove some programs at higher optimization levels, such as https://github.com/nexus-xyz/nexus-zkvm/blob/main/examples/src/bin/galeshapley.rs.

It would be good to explore the root causes of these PANICs, and try to improve the compilation pipeline so that we can successfully prove optimized programs (which should require fewer instructions and therefore be faster).