Add Pyodide support (#12731)
This includes some initial work on adding Pyodide support (issue
#12729). It is enough to get
```
uv pip compile -p /path/to/pyodide --extra-index-url file:/path/to/simple-index
```
to work which should already be quite useful.
## Test Plan
* added a unit test for `pyodide_platform`
* integration tested manually with:
```
cargo run pip install \
-p /home/rchatham/Documents/programming/tmp/pyodide-venv-test/.pyodide-xbuildenv-0.29.3/0.27.4/xbuildenv/pyodide-root/dist/python \
--extra-index-url file:/home/rchatham/Documents/programming/tmp/pyodide-venv-test/.pyodide-xbuildenv-0.29.3/0.27.4/xbuildenv/pyodide-root/package_index \
--index-strategy unsafe-best-match --target blah --no-build \
numpy pydantic
```
---------
Co-authored-by: konsti <konstin@mailbox.org>
Co-authored-by: Zanie Blue <contact@zanie.dev>
