- [ ] Have you followed the guidelines for contributing? - [ ] Have you signed the [CLA](http://www.ubuntu.com/legal/contributors/)? - [ ] Have you successfully run `make lint && make test`? --- Oxidizes the emitter class. The [PyO3 docs](https://pyo3.rs/v0.27.2/index.html) and [Maturin docs](https://www.maturin.rs/) may help with reviewing. So far, the only intended breaking change is the removal of the global `emit`. Rust, reasonably so, does not play nicely with globally mutable state or partially initialized variables. If anything else is breaking, it's either because it's not yet implemented or I didn't mean to break it, so definitely ask if you spot anything! Remaining work: - Streaming brief - `Emitter.open_stream` - External log handling (from `logging`) - Devise testing strategy - Incremental progress bars - Fix project versioning (see below) Overall structure --- In order to build with Maturin, the build backend just needed to be switched. This was mostly simple, but Maturin has an unfortunate limitation in that it completely lacks anything like `tool.setuptools_scm` for configuring tag-based dynamic versioning. This can be _mostly_ achieved via environment variables, but for local development builds with uv (`maturin develop --uv`), a version _must_ be present in `pyproject.toml`. For now, the version is hard-coded to `0.0.0+dev`. The field in `pyproject` setting the module name just makes the compiled `.so` appear with that import path. Otherwise, it would overwrite the Python portion of Craft CLI. This new submodule was named `_rs`. To test what has been done so far, clone this, update your venv, and then run `uv run maturin develop --uv`. This builds to a `.so`, then installs it as an editable wheel. Comments will be made on code in this PR for any other higher level design choices. CRAFT-4970