Create Level Generation Benchmark

[sunjay]

We should have a benchmark for the amount of time it takes to generate the 10 levels of the game. Use criterion.rs.

There are quite a few big opportunities for optimization that weren't taken for the sake of just getting things working at first. For example we currently regenerate the entire rooms graph every time when we should really only do it once and then keep it up to date. There are lots of such examples throughout the code and someone just needs to put in the effort to think about it.