Add support for pip-compile's `--unsafe-package` flag (#1889)
## Summary
In uv, we're going to use `--no-emit-package` for this, to convey that
the package will be included in the resolution but not in the output
file. It also mirrors flags like `--emit-index-url`.
We're also including an `--unsafe-package` alias.
Closes https://github.com/astral-sh/uv/issues/1415.
