Refactor fetchListIncrementally into RelayBatchFetcher and genericize timeout logic

Extracted `fetchListIncrementally` from `js/nostr/client.js` into a new `RelayBatchFetcher` class in `js/nostr/relayBatchFetcher.js` to reduce complexity in `NostrClient`.
Moved `withRequestTimeout` to `js/utils/asyncUtils.js` to make it reusable and remove duplication.
Updated `js/nostr/client.js` to use these new components while preserving existing behavior and specific logging for COUNT diagnostics.

- Created `js/nostr/relayBatchFetcher.js`
- Updated `js/utils/asyncUtils.js`
- Refactored `js/nostr/client.js`
- Verified with existing tests

Co-authored-by: PR0M3TH3AN <[email protected]>

js/utils/asyncUtils.js

@@ -1,3 +1,5 @@
+import { devLogger } from "./logger.js";
+
 /**
  * Maps over an iterable with a concurrency limit.
  *
@@ -51,3 +53,53 @@ export async function pMap(iterable, mapper, { concurrency = Infinity } = {}) {
     next();
   });
 }
+
+export function withRequestTimeout(promise, timeoutMs, onTimeout, message = "Request timed out") {
+  const resolvedTimeout = Number(timeoutMs);
+  const effectiveTimeout =
+    Number.isFinite(resolvedTimeout) && resolvedTimeout > 0
+      ? Math.floor(resolvedTimeout)
+      : 4000;
+
+  let timeoutId = null;
+  let settled = false;
+
+  return new Promise((resolve, reject) => {
+    timeoutId = setTimeout(() => {
+      if (settled) {
+        return;
+      }
+      settled = true;
+      if (typeof onTimeout === "function") {
+        try {
+          onTimeout();
+        } catch (cleanupError) {
+          devLogger.warn("[asyncUtils] Timeout cleanup failed:", cleanupError);
+        }
+      }
+      reject(new Error(message));
+    }, effectiveTimeout);
+
+    Promise.resolve(promise)
+      .then((value) => {
+        if (settled) {
+          return;
+        }
+        settled = true;
+        if (timeoutId) {
+          clearTimeout(timeoutId);
+        }
+        resolve(value);
+      })
+      .catch((error) => {
+        if (settled) {
+          return;
+        }
+        settled = true;
+        if (timeoutId) {
+          clearTimeout(timeoutId);
+        }
+        reject(error);
+      });
+  });
+}