Use windows registry to discover python (#6761)

Our current strategy of parsing the output of `py --list-paths` to get
the installed python versions on windows is brittle (#6524, missing
`py`, etc.) and it's slow (10ms last time i measured).

Instead, we should behave spec-compliant and read the python versions
from the registry following PEP 514.

It's not fully clear which errors we should ignore and which ones we
need to raise.

We're using the official rust-for-windows crates for accessing the
registry.

Fixes #1521
Fixes #6524

docs/concepts/python-versions.md

@@ -169,8 +169,8 @@ When searching for a Python version, the following locations are checked:
 - Managed Python installations in the `UV_PYTHON_INSTALL_DIR`.
 - A Python interpreter on the `PATH` as `python`, `python3`, or `python3.x` on macOS and Linux, or
   `python.exe` on Windows.
-- On Windows, the Python interpreter returned by `py --list-paths` that matches the requested
-  version.
+- On Windows, the Python interpreters in the Windows registry and Microsoft Store Python
+  interpreters (see `py --list-paths`) that match the requested version.
 
 In some cases, uv allows using a Python version from a virtual environment. In this case, the
 virtual environment's interpreter will be checked for compatibility with the request before