Research on Rust compiler optimization

[mattheworris]

Compiling polkadot takes a considerable amount of resources and time. This issue aims to investigate possible optimizations that could improve build times locally and in CI.

1. Basic research into how the Rust compiler works and how frequency uses build.rs and WASM to understand the bottlenecks. a. Document the current build process and any proposed optimizations.
2. Profiling of various build options, clean builds, re-builds, with caching, without caching, etc.
3. Design and execute experiments to determine whether proposed optimizations are efficient.