Async FS optimizations, exponential backoff, cleanup dedup and release v1.4.72

- Convert all sync FS ops (existsSync, readdirSync, statSync, writeFileSync,
  rmSync, renameSync) to async equivalents across download-manager, extractor,
  cleanup, storage, and logger to prevent UI freezes
- Replace linear retry delays with exponential backoff + jitter to prevent
  retry storms with many parallel downloads
- Deduplicate resolveArchiveItems into single shared function
- Replace Array.shift() O(N) in bandwidth chart with slice-based trimming
- Make logger rotation async in the async flush path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/renderer/App.tsx

@@ -239,8 +239,12 @@ const BandwidthChart = memo(function BandwidthChart({ items, running, paused }:
     history.push({ time: now, speed: paused ? 0 : totalSpeed });
 
     const cutoff = now - 60000;
-    while (history.length > 0 && history[0].time < cutoff) {
-      history.shift();
+    let trimIndex = 0;
+    while (trimIndex < history.length && history[trimIndex].time < cutoff) {
+      trimIndex += 1;
+    }
+    if (trimIndex > 0) {
+      speedHistoryRef.current = history.slice(trimIndex);
     }
 
     lastUpdateRef.current = now;