perf(nextcloud): read file as Uint8List

according to comment by a dart dev: https://stackoverflow.com/questions/73478943/flutter-dart-read-portions-of-file-as-bytes-rather-than-listint#comment129764806_73478943
it will allways return Uint8List
Signed-off-by: Nikolas Rimikis <rimikis.nikolas@gmail.com>

packages/nextcloud/lib/src/webdav/client.dart

@@ -189,7 +189,7 @@ class WebDavClient {
       file.openRead().map((final chunk) {
         uploaded += chunk.length;
         onProgress?.call(uploaded / fileStat.size);
-        return Uint8List.fromList(chunk);
+        return chunk as Uint8List;
       }),
       path,
       lastModified: lastModified,