Implement use of a custom fetch fn

src/modules/trains.ts

@@ -7,7 +7,7 @@ import { ValidationError } from '../lib/errors.js';
 export class TrainsModule {
     constructor(private client: BaseClient) { }
 
-    async getByHeadcode(headcode: string, date: string | Date = new Date, toc: string = ""): Promise<ApiResult<ApiTrainsTrainByHeadcode.TrainByHeadcodeResponse[]>> {
+    async getByHeadcode(headcode: string, date: string | Date = new Date, toc: string = "", customFetch?: typeof fetch): Promise<ApiResult<ApiTrainsTrainByHeadcode.TrainByHeadcodeResponse[]>> {
         if (!IsValidHeadcode(headcode)) {
             throw new ValidationError("headcode", "Invalid headcode format")
         }
@@ -29,6 +29,8 @@ export class TrainsModule {
 
         return this.client.request<ApiTrainsTrainByHeadcode.TrainByHeadcodeResponse[]>(path, {
             method: 'GET',
-        });
+        }, customFetch);
     }
+
+    async getByRid(rid: string, customFetch?: typeof fetch) {}
 }