chore(workspace): fix all clippy warnings in test code

Resolves 15 violations found by `cargo clippy --workspace --tests -D warnings`:
- Remove unused imports (Card, Rank) in cursor_plugin tests
- Replace absurd i32::MAX comparison with a meaningful >= 0 check
- Use range .contains() instead of manual >= && <= (manual_range_contains)
- Move impl FromRequestParts before test module in middleware.rs (items_after_test_module)
- Move _VEC3_REFERENCED const before test module in input_plugin.rs
- Convert runtime assert on constant to const { assert!(...) }
- Use .contains() instead of .iter().any() for slice membership
- Replace .get(...).is_none() with !.contains_key(...) in HashMap checks
- Collapse Default::default() + field assignment into struct literal initializers
  across solitaire_sync, solitaire_data, and solitaire_engine test helpers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_sync/src/stats.rs

@@ -135,17 +135,14 @@ mod tests {
 
     #[test]
     fn record_abandoned_resets_win_streak() {
-        let mut s = StatsSnapshot::default();
-        s.win_streak_current = 5;
+        let mut s = StatsSnapshot { win_streak_current: 5, ..Default::default() };
         s.record_abandoned();
         assert_eq!(s.win_streak_current, 0, "abandoned game must break the win streak");
     }
 
     #[test]
     fn record_abandoned_preserves_best_streak() {
-        let mut s = StatsSnapshot::default();
-        s.win_streak_best = 7;
-        s.win_streak_current = 7;
+        let mut s = StatsSnapshot { win_streak_best: 7, win_streak_current: 7, ..Default::default() };
         s.record_abandoned();
         assert_eq!(s.win_streak_best, 7, "best streak must not be reduced on abandon");
         assert_eq!(s.win_streak_current, 0);