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_core/src/scoring.rs

@@ -91,6 +91,6 @@ mod tests {
     fn time_bonus_is_capped_at_i32_max_for_huge_values() {
         // Very short elapsed time would overflow without the .min() guard.
         let bonus = compute_time_bonus(1);
-        assert!(bonus <= i32::MAX, "time bonus must fit in i32");
+        assert!(bonus >= 0, "time bonus must be non-negative after u64→i32 cast");
     }
 }