Local builds with pixi

Setting up a local build environment for emscripten-forge used to be a very complicated process with many dependencies and many steps. But with the usage of pixi this has become trivial!

# this only needs to be done once
pixi run setup

# thats it! packages can now be built
pixi run build-emscripten-wasm32-pkg recipes/recipes_emscripten/regex

Goodby boa, welcome rattler-build   Rust/PyO3 Support