## Summary
In preview mode on windows, register und un-register the managed python build standalone installations in the Windows registry following PEP 514.
We write the values defined in the PEP plus the download URL and hash. We add an entry when installing a version, remove an entry when uninstalling and removing all values when uninstalling with `--all`. We update entries only by overwriting existing values, there is no "syncing" involved.
Since they are not official builds, pbs gets a prefix. `py -V:Astral/CPython3.13.1` works, `py -3.13` doesn't.
```
$ py --list-paths
-V:3.12 * C:\Users\Konsti\AppData\Local\Programs\Python\Python312\python.exe
-V:3.11.9 C:\Users\Konsti\.pyenv\pyenv-win\versions\3.11.9\python.exe
-V:3.11 C:\Users\micro\AppData\Local\Programs\Python\Python311\python.exe
-V:3.8 C:\Users\micro\AppData\Local\Programs\Python\Python38\python.exe
-V:Astral/CPython3.13.1 C:\Users\Konsti\AppData\Roaming\uv\data\python\cpython-3.13.1-windows-x86_64-none\python.exe
```
Registry errors are reported but not fatal, except for operations on the company key since it's not bound to any specific python interpreter.
On uninstallation, we prune registry entries that have no matching Python installation (i.e. broken entries).
The code uses the official `windows_registry` crate of the `winreg` crate.
Best reviewed commit-by-commit.
## Test Plan
We're reusing an existing system check to test different (un)installation scenarios.
