Draft: Hashed and cached build

This is a proof of concept for making the build system on the CI hash the input files and only re-build the necessary parts even when they are populated from a cache. This should give use very fast CI builds.

It does rely however on a fork of the ninja executable. The source of this fork is in my repo on Github. The changes were mostly made on a pull-request to ninja almost 5 years ago which was rejected. I don't mind maintaining a fork though as I use Ninja for other projects that could benefit from input file hashing too.

(based on !155 (merged) as it's changing build.py too and adding argument parsing)