test(mc-turn): ✅ Add serde roundtrip tests for JSON ↔ Rust struct validation

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/simulator/crates/mc-turn/tests/serde_roundtrip.rs

@@ -373,6 +373,8 @@ fn trade_ledger_diplomatic_agreement_roundtrip() {
                     eta_turn: Some(15),
                     delivered: false,
                     intercepted: false,
+                    planned_path: Vec::new(),
+                    path_step: 0,
                 }),
             }),
         ],