Passing `--python-platform` flag to `uv`

[sondr3]

Related to #717 and #1053, now that uv is the default backend would it be possible to pass the --python-platform flag either as configuration or its flag for sync/add etc? This would get us 95% of the way for platform agnostic lockfiles as we only really care about locking down dependencies for Linux.

[bobbyrenwick]

Are there plans to expose the --universal flag that came to uv recently?

[impredicative]

This works:

[tool.rye]
universal = true