Add a common abstraction to discover PEP 723 script interpreters (#10132)

## Summary

This logic is already repeated twice, and I'm on the verge of adding a
third.

(No behavioral changes.)

crates/uv-python/src/installation.rs

@@ -229,6 +229,7 @@ impl PythonInstallation {
         &self.interpreter
     }
 
+    /// Consume the [`PythonInstallation`] and return the [`Interpreter`].
     pub fn into_interpreter(self) -> Interpreter {
         self.interpreter
     }