feat: initial Earthly CI

[ludamad]

Introduces earthly as an alternative CI that hopes to eventually replace our current build-system.

https://docs.earthly.dev/ is a build system that combines Makefiles and Dockerfiles. This is basically exactly what our system needed, IMO, and has some nice things figured out. Hope is to reduce complexity of working with the build system by a good chunk.

Core changes:

• we have a github actions CI that runs a single end to end test inside earthly for arm64 and x86_64
• new Earthfile's now mirror the Dockerfile's, notable differences:
  • we build our own foundry package for ARM support
  • we build our own wasi-sdk package for ARM support
  • grumpkin SRS is no longer generated on the spot, but downloaded like bn254 SRS
  • we don't inject any commit hashes for Noir as this would cause spurious rebuilds as any difference stops caching, instead we inject a content hash (to be revisited)

Side changes:

• since we build our own wasi-sdk 21 package, and it is clang18, some compilation workarounds
• allow specifying a different nargo and acvm binary in build
• small output tweaks