Add support for managed installs of free-threaded Python (#8100)
Closes https://github.com/astral-sh/uv/issues/7193
```
❯ cargo run -q -- python uninstall 3.13t
Searching for Python versions matching: Python 3.13t
Uninstalled Python 3.13.0 in 231ms
- cpython-3.13.0+freethreaded-macos-aarch64-none
❯ cargo run -q -- python install 3.13t
Searching for Python versions matching: Python 3.13t
Installed Python 3.13.0 in 3.54s
+ cpython-3.13.0+freethreaded-macos-aarch64-none
❯ cargo run -q -- python install 3.12t
Searching for Python versions matching: Python 3.12t
error: No download found for request: cpython-3.12t-macos-aarch64-none
❯ cargo run -q -- python install 3.13rc3t
Searching for Python versions matching: Python 3.13rc3t
Found existing installation for Python 3.13rc3t: cpython-3.13.0+freethreaded-macos-aarch64-none
❯ cargo run -q -- run -p 3.13t python -c "import sys; print(sys.base_prefix)"
/Users/zb/.local/share/uv/python/cpython-3.13.0+freethreaded-macos-aarch64-none
```
