## 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.
## Summary
This PR declares and documents all environment variables that are used
in one way or another in `uv`, either internally, or externally, or
transitively under a common struct.
I think over time as uv has grown there's been many environment
variables introduced. Its harder to know which ones exists, which ones
are missing, what they're used for, or where are they used across the
code. The docs only documents a handful of them, for others you'd have
to dive into the code and inspect across crates to know which crates
they're used on or where they're relevant.
This PR is a starting attempt to unify them, make it easier to discover
which ones we have, and maybe unlock future posibilities in automating
generating documentation for them.
I think we can split out into multiple structs later to better organize,
but given the high influx of PR's and possibly new environment variables
introduced/re-used, it would be hard to try to organize them all now
into their proper namespaced struct while this is all happening given
merge conflicts and/or keeping up to date.
I don't think this has any impact on performance as they all should
still be inlined, although it may affect local build times on changes to
the environment vars as more crates would likely need a rebuild. Lastly,
some of them are declared but not used in the code, for example those in
`build.rs`. I left them declared because I still think it's useful to at
least have a reference.
Did I miss any? Are their initial docs cohesive?
Note, `uv-static` is a terrible name for a new crate, thoughts? Others
considered `uv-vars`, `uv-consts`.
## Test Plan
Existing tests
Microsoft Store Pythons do not always register themselves in the
registry, so we port
<58ce131037/PC/launcher2.c (L1744)>
and look them up on the filesystem in known locations.
## Test Plan
So far I've confirmed that we find a store Python when I use `cargo run
python list`, can we make this a part of any of the platform tests
maybe?
