Remove separate test files in favor of same-file mod tests (#9199)

## Summary

These were moved as part of a broader refactor to create a single
integration test module. That "single integration test module" did
indeed have a big impact on compile times, which is great! But we aren't
seeing any benefit from moving these tests into their own files (despite
the claim in [this blog
post](https://matklad.github.io/2021/02/27/delete-cargo-integration-tests.html),
I see the same compilation pattern regardless of where the tests are
located). Plus, we don't have many of these, and same-file tests is such
a strong Rust convention.

crates/uv-python/src/python_version.rs

@@ -168,4 +168,37 @@ impl PythonVersion {
 }
 
 #[cfg(test)]
-mod tests;
+mod tests {
+    use std::str::FromStr;
+
+    use uv_pep440::{Prerelease, PrereleaseKind, Version};
+
+    use crate::PythonVersion;
+
+    #[test]
+    fn python_markers() {
+        let version = PythonVersion::from_str("3.11.0").expect("valid python version");
+        assert_eq!(version.python_version(), Version::new([3, 11]));
+        assert_eq!(version.python_version().to_string(), "3.11");
+        assert_eq!(version.python_full_version(), Version::new([3, 11, 0]));
+        assert_eq!(version.python_full_version().to_string(), "3.11.0");
+
+        let version = PythonVersion::from_str("3.11").expect("valid python version");
+        assert_eq!(version.python_version(), Version::new([3, 11]));
+        assert_eq!(version.python_version().to_string(), "3.11");
+        assert_eq!(version.python_full_version(), Version::new([3, 11, 0]));
+        assert_eq!(version.python_full_version().to_string(), "3.11.0");
+
+        let version = PythonVersion::from_str("3.11.8a1").expect("valid python version");
+        assert_eq!(version.python_version(), Version::new([3, 11]));
+        assert_eq!(version.python_version().to_string(), "3.11");
+        assert_eq!(
+            version.python_full_version(),
+            Version::new([3, 11, 8]).with_pre(Some(Prerelease {
+                kind: PrereleaseKind::Alpha,
+                number: 1
+            }))
+        );
+        assert_eq!(version.python_full_version().to_string(), "3.11.8a1");
+    }
+}