Discover Microsoft Store Pythons (#6807)

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?

crates/uv-python/src/lib.rs

@@ -26,6 +26,8 @@ mod installation;
 mod interpreter;
 mod libc;
 pub mod managed;
+#[cfg(windows)]
+mod microsoft_store;
 pub mod platform;
 mod pointer_size;
 mod prefix;