Separated and improved request throttling.

src/fetch/item.js

@@ -8,7 +8,7 @@ const phash = require('sharp-phash');
 
 const { agentFor } = require('../proxy');
 const logger = require('../logger')(__filename);
-const limiter = require('../limiter').items;
+const limiterFor = require('../limiter');
 
 // bhttp has no timeout at all by default - if the server (or, more likely, a proxy tunnel
 // that connects fine but then never relays anything) just stops responding mid-request without
@@ -42,7 +42,7 @@ async function fetchItem(url, attempt, context) {
         // whichever of proxied/direct is NOT what it'd normally get - see resolveProxyUrl()
         const flip = config.proxy.retryFlipped && attempt > 0;
 
-        const res = await limiter.schedule(async () => withTimeout(
+        const res = await limiterFor(url).schedule(async () => withTimeout(
             bhttp.get(url, { headers: context.headers, agent: agentFor(url, { flip }) }),
             config.fetch.timeout,
             url,