perf(miner): abort xmrig stat fetches on stop

The miner's stats and pool-API fetches are blocking HTTP calls on the
monitor thread with multi-second timeouts. When the miner was stopped,
stop() still had to wait out an in-flight request before the monitor
thread could join.

- Both fetches now install a curl progress callback that aborts the
  transfer as soon as a stop is requested, so a request in flight ends
  promptly instead of running down its timeout.
- An abort triggered by stop is treated as a clean cancellation, not a
  fetch failure, so it is not logged or counted against the failure
  warning.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/daemon/xmrig_manager.cpp

@@ -745,12 +745,16 @@ void XmrigManager::fetchStatsHttp() {
     curl_easy_setopt(curl, CURLOPT_TIMEOUT_MS, 2000L);       // 2s timeout — generous for loaded system
     curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT_MS, 1000L); // 1s connect timeout
     curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1L);            // Avoid signal issues in threads
+    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);
+    curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, &XmrigManager::abortCb);
+    curl_easy_setopt(curl, CURLOPT_XFERINFODATA, this);
 
     CURLcode res = curl_easy_perform(curl);
     curl_slist_free_all(headers);
     curl_easy_cleanup(curl);
 
     if (res != CURLE_OK) {
+        if (should_stop_.load()) return;  // aborted by stop(): not a failure
         static int s_fail_count = 0;
         if (++s_fail_count <= 5 || s_fail_count % 30 == 0) {
             DEBUG_LOGF("[WARN] XmrigManager::pollStats: curl failed (%d): %s  url=%s\n",
@@ -845,6 +849,9 @@ void XmrigManager::fetchPoolApiStats() {
     // pool.dragonx.cc sits behind Cloudflare and 403s odd User-Agents.
     curl_easy_setopt(curl, CURLOPT_USERAGENT, "Mozilla/5.0 (compatible; ObsidianDragon)");
     curl_easy_setopt(curl, CURLOPT_ACCEPT_ENCODING, "");
+    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);
+    curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, &XmrigManager::abortCb);
+    curl_easy_setopt(curl, CURLOPT_XFERINFODATA, this);
 
     CURLcode res = curl_easy_perform(curl);
     curl_easy_cleanup(curl);