Trim injected python_version marker to (major, minor) (#2395)

## Summary

Per [PEP 508](https://peps.python.org/pep-0508/), `python_version` is
just major and minor:

![Screenshot 2024-03-12 at 5 15
09 PM](https://github.com/astral-sh/uv/assets/1309177/cc3b8d65-dab3-4229-aed7-c6fe590b8da0)

Right now, we're using the provided version directly, so if it's, e.g.,
`-p 3.11.8`, we'll inject the wrong marker. This was causing `pandas` to
omit `numpy` when `-p 3.11.8` was provided, since its markers look like:

```
Requires-Dist: numpy<2,>=1.22.4; python_version < "3.11"
Requires-Dist: numpy<2,>=1.23.2; python_version == "3.11"
Requires-Dist: numpy<2,>=1.26.0; python_version >= "3.12"
```

Closes https://github.com/astral-sh/uv/issues/2392.

crates/uv-resolver/src/python_requirement.rs

@@ -1,32 +1,31 @@
-use pep440_rs::Version;
-use pep508_rs::MarkerEnvironment;
+use pep508_rs::{MarkerEnvironment, StringVersion};
 use uv_interpreter::Interpreter;
 
-#[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Debug, Clone, Eq, PartialEq)]
 pub struct PythonRequirement {
     /// The installed version of Python.
-    installed: Version,
+    installed: StringVersion,
     /// The target version of Python; that is, the version of Python for which we are resolving
     /// dependencies. This is typically the same as the installed version, but may be different
     /// when specifying an alternate Python version for the resolution.
-    target: Version,
+    target: StringVersion,
 }
 
 impl PythonRequirement {
     pub fn new(interpreter: &Interpreter, markers: &MarkerEnvironment) -> Self {
         Self {
-            installed: interpreter.python_version().clone(),
-            target: markers.python_full_version.version.clone(),
+            installed: interpreter.python_full_version().clone(),
+            target: markers.python_full_version.clone(),
         }
     }
 
     /// Return the installed version of Python.
-    pub fn installed(&self) -> &Version {
+    pub fn installed(&self) -> &StringVersion {
         &self.installed
     }
 
     /// Return the target version of Python.
-    pub fn target(&self) -> &Version {
+    pub fn target(&self) -> &StringVersion {
         &self.target
     }
 }