uv-resolver: error during installation for conflicting extras

This collects ALL activated extras while traversing the lock file to
produce a `Resolution` for installation. If any two extras are activated
that are conflicting, then an error is produced.

We add a couple of tests to demonstrate the behavior. One case is
desirable (where we conditionally depend on `package[extra]`) and the
other case is undesirable (where we create an uninstallable lock file).

Fixes #9942, Fixes #10590

crates/uv-resolver/src/lock/mod.rs

@@ -4897,6 +4897,16 @@ enum LockErrorKind {
         #[source]
         err: uv_distribution::Error,
     },
+    #[error(
+        "Found conflicting extras `{package1}[{extra1}]` \
+         and `{package2}[{extra2}]` enabled simultaneously"
+    )]
+    ConflictingExtra {
+        package1: PackageName,
+        extra1: ExtraName,
+        package2: PackageName,
+        extra2: ExtraName,
+    },
 }
 
 /// An error that occurs when a source string could not be parsed.