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-cli/src/comma.rs

@@ -60,4 +60,66 @@ impl FromStr for CommaSeparatedRequirements {
 }
 
 #[cfg(test)]
-mod tests;
+mod tests {
+    use super::CommaSeparatedRequirements;
+    use std::str::FromStr;
+
+    #[test]
+    fn single() {
+        assert_eq!(
+            CommaSeparatedRequirements::from_str("flask").unwrap(),
+            CommaSeparatedRequirements(vec!["flask".to_string()])
+        );
+    }
+
+    #[test]
+    fn double() {
+        assert_eq!(
+            CommaSeparatedRequirements::from_str("flask,anyio").unwrap(),
+            CommaSeparatedRequirements(vec!["flask".to_string(), "anyio".to_string()])
+        );
+    }
+
+    #[test]
+    fn empty() {
+        assert_eq!(
+            CommaSeparatedRequirements::from_str("flask,,anyio").unwrap(),
+            CommaSeparatedRequirements(vec!["flask".to_string(), "anyio".to_string()])
+        );
+    }
+
+    #[test]
+    fn single_extras() {
+        assert_eq!(
+            CommaSeparatedRequirements::from_str("psycopg[binary,pool]").unwrap(),
+            CommaSeparatedRequirements(vec!["psycopg[binary,pool]".to_string()])
+        );
+    }
+
+    #[test]
+    fn double_extras() {
+        assert_eq!(
+            CommaSeparatedRequirements::from_str("psycopg[binary,pool], flask").unwrap(),
+            CommaSeparatedRequirements(vec![
+                "psycopg[binary,pool]".to_string(),
+                "flask".to_string()
+            ])
+        );
+    }
+
+    #[test]
+    fn single_specifiers() {
+        assert_eq!(
+            CommaSeparatedRequirements::from_str("requests>=2.1,<3").unwrap(),
+            CommaSeparatedRequirements(vec!["requests>=2.1,<3".to_string(),])
+        );
+    }
+
+    #[test]
+    fn double_specifiers() {
+        assert_eq!(
+            CommaSeparatedRequirements::from_str("requests>=2.1,<3, flask").unwrap(),
+            CommaSeparatedRequirements(vec!["requests>=2.1,<3".to_string(), "flask".to_string()])
+        );
+    }
+}