Refactor endpoints/chats.js

1. Move formatBytes utility to util.js
2. Fix type error related to dates sorting
3. Add type to backupFunctions map

src/util.js

@@ -142,6 +142,19 @@ export function getHexString(length) {
     return result;
 }
 
+/**
+ * Formats a byte size into a human-readable string with units
+ * @param {number} bytes - The size in bytes to format
+ * @returns {string} The formatted string (e.g., "1.5 MB")
+ */
+export function formatBytes(bytes) {
+    if (bytes === 0) return '0 B';
+    const k = 1024;
+    const sizes = ['B', 'KB', 'MB', 'GB'];
+    const i = Math.floor(Math.log(bytes) / Math.log(k));
+    return parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i];
+}
+
 /**
  * Extracts a file with given extension from an ArrayBuffer containing a ZIP archive.
  * @param {ArrayBuffer} archiveBuffer Buffer containing a ZIP archive