Add in-memory caching for online count, enable compression, and add staleTimes for router cache

src/lib/cache.ts

@@ -0,0 +1,17 @@
+type CacheEntry<T> = { data: T; expiresAt: number };
+const store = new Map<string, CacheEntry<unknown>>();
+
+export function cached<T>(key: string, ttlMs: number, fn: () => Promise<T>): Promise<T> {
+  const existing = store.get(key);
+  if (existing && existing.expiresAt > Date.now()) {
+    return Promise.resolve(existing.data as T);
+  }
+  return fn().then((data) => {
+    store.set(key, { data, expiresAt: Date.now() + ttlMs });
+    return data;
+  });
+}
+
+export function bustCache(key: string): void {
+  store.delete(key);
+}