Add caching

[sam-writer]

streamlit supports caching... maybe this would be a good idea to speed things up?

Streamlit caching docs

[quinn-dougherty]

This will follow trivially from wrapping key operations in functions as discussed here https://github.com/pennsignals/chime/issues/6#issuecomment-600214043 -- note caching is not the sort of side effect that limits modularity in my experience.