✅ Wave 112: Test suite improvements and fixes

- Rewrote audit_compliance.rs: Proper behavior tests (no stubs) - Agent 9, 19
- Enhanced audit_trail_persistence_test.rs: Comprehensive persistence validation
- Fixed audit_trails.rs: Improved error handling and event processing
- Updated rate limiter tests: Result unwrapping and stress test improvements
- Optimized full_trading_cycle.rs benchmark: Better performance measurement
- All tests follow anti-workaround protocol (no placeholders, actual validations)

trading_engine/src/compliance/audit_trails.rs

@@ -247,7 +247,7 @@ pub struct PerformanceMetrics {
 }
 
 /// Risk levels for audit events
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 /// RiskLevel
 ///
 /// Auto-generated documentation placeholder - enhance with specifics
@@ -795,8 +795,28 @@ pub struct AuditTrailQuery {
     pub sort_order: SortOrder,
 }
 
+impl Default for AuditTrailQuery {
+    fn default() -> Self {
+        Self {
+            start_time: chrono::Utc::now() - chrono::Duration::hours(24),
+            end_time: chrono::Utc::now(),
+            event_types: None,
+            transaction_id: None,
+            order_id: None,
+            actor: None,
+            symbol: None,
+            account_id: None,
+            risk_level: None,
+            compliance_tags: None,
+            limit: Some(100),
+            offset: None,
+            sort_order: SortOrder::default(),
+        }
+    }
+}
+
 /// Sort order for queries
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
 /// SortOrder
 ///
 /// Auto-generated documentation placeholder - enhance with specifics
@@ -804,6 +824,7 @@ pub enum SortOrder {
     /// Ascending by timestamp
     TimestampAsc,
     /// Descending by timestamp
+    #[default]
     TimestampDesc,
     /// By event type
     EventType,