[wip] preprocessor PoC

[klkvr]

ref #197

Implements preprocessor allowing us to skip recompiling tests on non-interface source file changes. Still testing, but looks like it's working correctly, decreasing single-change build times from ~1 minute to 5s in some cases.

Implementation needed some hacks to correctly handle constructor arguments, tried to document it clearly - https://github.com/foundry-rs/compilers/blob/15ce120c2e17aa384a43af79a202a36ac78a0c6f/crates/compilers/src/preprocessor.rs#L265

still WIP as caching changes are not opt-in yet (preprocessor is), and I want to do more testing