refactor(usage): shape sources as fetch functions

Keep the plugin usage API limited to stable report and presentation helpers. Source-local parsers and timeout handling preserve credential and response parity while the cases move alongside each source.

packages/server/src/plugins/copilot-usage-source/index.server.ts

@@ -1,6 +1,6 @@
 import type { PluginServerContext } from "@getpaseo/plugin/server";
 import { inputSchema } from "./shared/input.js";
-import { CopilotQuotaProvider } from "./server/usage.js";
+import { fetchUsage } from "./server/usage.js";
 
 export default function contribute(server: PluginServerContext) {
   server.registerUsageSource({
@@ -9,7 +9,7 @@ export default function contribute(server: PluginServerContext) {
     icon: "icon.svg",
     input: inputSchema,
     discover: async () => [{}],
-    fetch: async (_input) => new CopilotQuotaProvider({ logger: console }).fetchUsage(),
+    fetch: fetchUsage,
   });
   return () => {};
 }