Write out full PEP 508 requirements for relative paths and editables

[charliermarsh]

In pip compile, we take special care to write out editables and relative paths as unnamed URLs. But uv supports PEP 508 requirements for editables, and allows relative URLs too. Should we just write them out in full form? The output requirements.txt won't work with pip, since pip does not yet support PEP 508 for editables, so we'd need to have a --pip-compat flag or similar to allow that behavior.

[charliermarsh]

Concretely, see RequirementsTxtDist::to_requirements_txt. In theory, we shouldn't need that special-casing. We can write -e for an editable, then write a PEP 508 requirement in either case.