diigo-cache: pace diigo calls only; cache hits don't wait

page() ran the 500 ms pacing gate before the cache check, so every hit
waited too: a fill rerun skipping 166 cached pages took ~80 s and
looked like a start from scratch. The gate now sits after the hit
check (re-checking storage once through it, in case a request ahead
had just etched the page).

Regression test: the fixed-clock test cache records its sleeps; a miss
sleeps once, three hits add none (failed before: 4 sleeps).

Generated-by: Claude Opus 5.5

diigo-cache/tests/test-worker.ts

@@ -12,8 +12,23 @@ export { default } from "../src/index.js";
 /** 2026-10-07T12:00:00Z */
 export const FIXED_NOW = Date.UTC(2026, 9, 7, 12, 0, 0);
 
+/** a fixed clock that records each sleep it is asked for */
 export class FixedClockCache extends DiigoCacheLogic {
+	#sleeps: number[] = [];
+
 	constructor(ctx: DurableObjectState, env: CacheEnv) {
-		super(ctx, env, { now: () => FIXED_NOW, sleep: async () => {} });
+		const sleeps: number[] = [];
+		super(ctx, env, {
+			now: () => FIXED_NOW,
+			sleep: async (ms) => {
+				sleeps.push(ms);
+			},
+		});
+		this.#sleeps = sleeps;
+	}
+
+	/** the sleeps so far (test hook) */
+	async sleeps(): Promise<number[]> {
+		return [...this.#sleeps];
 	}
 }