feat: split client to separate class

libraries/adapter.ts

@@ -0,0 +1,12 @@
+import type { RouteMethod } from "./route.ts";
+
+export type RelayAdapter = {
+  fetch(input: RequestInput): Promise<unknown>;
+};
+
+export type RequestInput = {
+  method: RouteMethod;
+  url: string;
+  search: string;
+  body?: string;
+};