Rename PythonRequest::Any -> PythonRequest::Default (#7514)

As we support more complex Python discovery behaviors such as:

- #7431 
- #7335 
- #7300 

`Any` is no longer accurate, we actually are looking for a reasonable
default Python version to use which may exclude the first one we find.
Separately, we need the idea of `Any` to improve behavior when listing
versions (e.g., #7286) where we do actually want to match _any_ Python
version. As a first step, we'll rename `Any` to `Default`. Then, we'll
introduce a new `Any` that actually behaves as we'd expect.

crates/uv-python/src/installation.rs

@@ -87,7 +87,7 @@ impl PythonInstallation {
         cache: &Cache,
         reporter: Option<&dyn Reporter>,
     ) -> Result<Self, Error> {
-        let request = request.unwrap_or_else(|| &PythonRequest::Any);
+        let request = request.unwrap_or_else(|| &PythonRequest::Default);
 
         // Search for the installation
         match Self::find(request, environments, preference, cache) {