fix: resolve all Rust test compile warnings without suppression

Remove unused imports and a dead test helper, and strengthen tests that
held unused bindings/fields so the values are actually exercised:
- drop unused imports (HttpConfig, MediaType, std::io::Write)
- remove unused TestEventEmitter::clear helper
- replace meaningless size_of asserts with real empty-manager checks
- assert on MockTrack.name in sorting tests

src-tauri/src/commands/player/mod.rs

@@ -1796,6 +1796,7 @@ mod tests {
         // Test finding track 1 (should be index 0)
         let index1 = tracks.iter().position(|t| t.id == "track1");
         assert_eq!(index1, Some(0), "Track 1 should be at index 0");
+        assert_eq!(tracks[0].name, "Song 1", "Track at index 0 should carry its name");
 
         // Test finding track 3 (should be index 2)
         let index3 = tracks.iter().position(|t| t.id == "track3");
@@ -1869,6 +1870,7 @@ mod tests {
 
         // Verify all tracks are in correct order
         assert_eq!(tracks[0].id, "id1");
+        assert_eq!(tracks[0].name, "Track 1", "Sorted track should retain its name");
         assert_eq!(tracks[1].id, "id2");
         assert_eq!(tracks[2].id, "id3");
         assert_eq!(tracks[3].id, "id4");