Fixes#11217
By default, a 64-bit uv does not see a 32-bit global (HKLM) installation
of Python in the registry
(https://github.com/astral-sh/uv/issues/11217). To work around this, we
manually request both 32-bit and 64-bit access using registry access
flags (https://peps.python.org/pep-0514/#sample-code). The flags have no
effect on 32-bit (https://stackoverflow.com/a/12796797/3549270).
This effect is that there is an asymmetry between discovery modes: For
the registry-based discovery using PEP 514, we discover both 32-bit and
64-bit Pythons, while for managed installations, we are stricter and
only discover those matching in bit-ness.
I tested this manually with an additional 32-bit installation of CPython
on a 64-bit machine and windows with 32-bit and 64-bit (x86_64 and i686)
builds of uv.
## 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.
