Address coderabbit feedback

Signed-off-by: Dave Thaler <[email protected]>

OrcanodeMonitor/Core/Fetcher.cs

@@ -941,6 +941,11 @@ private static void AddHydrophoneStreamStatusEvent(OrcanodeMonitorContext contex
             return await GetExactAudioSampleAsync(node, newUri, logger);
         }
 
+        /// <summary>
+        /// Retrieves the last modified date of a resource via HTTP HEAD request.
+        /// </summary>
+        /// <param name="uri">The URI of the resource to check.</param>
+        /// <returns>The last modified date in UTC, or null if not available.</returns>
         public async static Task<DateTime?> GetLastModifiedAsync(Uri uri)
         {
             using var headRequest = new HttpRequestMessage(HttpMethod.Head, uri);