refactor: declare GM_fetch as global for typescript

important for the compiler when mocking for unit tests

global.d.ts

@@ -0,0 +1,7 @@
+export {};
+
+declare global {
+  interface Window {
+    GM_fetch: typeof fetch; // or a more specific custom type
+  }
+}

tsconfig.json

@@ -1,4 +1,5 @@
 {
+  "include": ["src/**/*", "declarations.d.ts", "global.d.ts"],
   "compilerOptions": {
     "outDir": "./dist/",
     "noImplicitAny": true,