Report Python versions in pyvenv.cfg version mismatch (#13027)

When working on #13025 I noticed this message was lacking versions,
which seems frustrating if you're debugging things.

I refactored the general `matches_interpreter` utilities that were added
in https://github.com/astral-sh/uv/pull/12884 into a more purpose-fit
function that returns an `Option` with the versions if there's a
mismatch.

crates/uv-python/src/python_version.rs

@@ -8,6 +8,12 @@ use uv_pep508::{MarkerEnvironment, StringVersion};
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct PythonVersion(StringVersion);
 
+impl From<StringVersion> for PythonVersion {
+    fn from(version: StringVersion) -> Self {
+        Self(version)
+    }
+}
+
 impl Deref for PythonVersion {
     type Target = StringVersion;
 
@@ -176,6 +182,11 @@ impl PythonVersion {
         &self.0.version
     }
 
+    /// Return the full parsed Python version.
+    pub fn into_version(self) -> Version {
+        self.0.version
+    }
+
     /// Return the major version of this Python version.
     pub fn major(&self) -> u8 {
         u8::try_from(self.0.release().first().copied().unwrap_or(0)).expect("invalid major version")