Deduplicate when install or uninstall python

[j178]

When specifying the same argument multiple times, the same version will be downloaded multiple times:

$ cargo run -- python install --preview --force 3.12.3 cpython-3.12 3.12.3 3.12
Looking for installation Python 3.12.3 (any-3.12.3-any-any-any)
Looking for installation cpython-3.12-any-any-any (cpython-3.12-any-any-any)
Looking for installation Python 3.12.3 (any-3.12.3-any-any-any)
Looking for installation Python 3.12 (any-3.12-any-any-any)
Found 4/4 versions requiring installation
Downloading cpython-3.12.3-windows-x86_64-none
Downloading cpython-3.12.3-windows-x86_64-none
Downloading cpython-3.12.3-windows-x86_64-none
Downloading cpython-3.12.3-windows-x86_64-none

This PR deduplicates the ManagedPythonDownload before install or uninstall:

$ cargo run -q -- python install --preview --force 3.12.3 cpython-3.12 3.12.3 3.12
Looking for installation Python 3.12 (any-3.12-any-any-any)
Looking for installation Python 3.12.3 (any-3.12.3-any-any-any)
Looking for installation cpython-3.12-any-any-any (cpython-3.12-any-any-any)
Downloading cpython-3.12.3-windows-x86_64-none
Installed Python 3.12.3 to C:\Users\nigel\AppData\Roaming\uv\data\python\cpython-3.12.3-windows-x86_64-none
Installed 1 version in 6s

$ cargo run -q -- python uninstall --preview  3.12.3 cpython-3.12 3.12.3 3.12
Looking for Python installations matching Python 3.12 (any-3.12-any-any-any)
Found installation `cpython-3.12.3-windows-x86_64-none` that matches Python 3.12
Looking for Python installations matching Python 3.12.3 (any-3.12.3-any-any-any)
Looking for Python installations matching cpython-3.12-any-any-any (cpython-3.12-any-any-any)
Uninstalled `cpython-3.12.3-windows-x86_64-none`
Removed 1 Python installation

[zanieb]

We probably need to de-duplicate the keys we're going to download too

[charliermarsh]

Thanks, your contributions are great.