feat(api-gdext): ✨ Introduce pending tile improvement tracking in GdGameState with new fields/methods for monitoring and managing improvements

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

src/simulator/api-gdext/src/lib.rs

@@ -1930,6 +1930,8 @@ impl IRefCounted for GdGameState {
                 pending_formation_shapes: Default::default(),
                 pending_split_requests: Default::default(),
                 pending_auto_join_requests: Default::default(),
+                tile_improvements: Default::default(),
+                improvement_registry: Default::default(),
             },
             base,
         }