Refactor Railroad and TrainStation classes to improve railroad management

- Replaced direct deletion of railroads with dedicated methods in TrainStation for better encapsulation.
- Added a mapping for quick lookup of railroads by neighboring stations.
- Updated clearRailroads and addRailroad methods to maintain consistency in railroad management.

src/core/game/TrainStation.ts

@@ -139,7 +139,6 @@ export class TrainStation {
   private railroads: Set<Railroad> = new Set();
   // Quick lookup from neighboring station to connecting railroad
   private railroadByNeighbor: Map<TrainStation, Railroad> = new Map();
-
   // Batman routing properties - now using IDs for memory efficiency
   private routingTable: Map<number, RoutingEntry> = new Map();
   private sequenceNumber: number = 0;