Avoid canonicalizing user-provided interpreters (#2072)
## Summary
We shouldn't be resolving symlinks on the provided interpreter;
otherwise we break `pyenv`, since running `cargo run pip install mypy
--python .venv/bin/python` will immediately resolve to (e.g.)
`/Users/crmarsh/.pyenv/versions/3.10.2/bin/python3.10`, and pyenv relies
on the path to do its lookups.
Instead, the canonicalizing happens when we query the interpreter
metadata.
Closes https://github.com/astral-sh/uv/issues/2068.
## Test Plan
Ran `cargo run pip install mypy --python .venv/bin/python -v -n` with a
virtualenv created using a pyenv Python; verified that Mypy was
installed into the virtual environment, rather than into the global
environment.
