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/environment.rs

@@ -80,7 +80,7 @@ impl fmt::Display for EnvironmentNotFound {
             EnvironmentPreference::OnlyVirtual => SearchType::Virtual,
         };
 
-        if matches!(self.request, PythonRequest::Any) {
+        if matches!(self.request, PythonRequest::Default) {
             write!(f, "No {search_type} found")?;
         } else {
             write!(f, "No {search_type} found for {}", self.request)?;