Early extraction of duration metadata via playlist thumbnail overlay

Early gathering of item video durations from playlist metadata, prior to downloading individual item metadata pages, so that video duration values are (e.g.) shown in `--flat-playlist` or `--simulate`, and/or can be used as a download filtering criterion.

youtube_dl/extractor/youtube.py

@@ -315,7 +315,7 @@ class YoutubeBaseInfoExtractor(InfoExtractor):
              lambda x: x['title']['simpleText']), compat_str)
         description = try_get(
             renderer, lambda x: x['descriptionSnippet']['runs'][0]['text'],
-            compat_str) 
+            compat_str)
         duration_text = try_get(
             renderer,
             (lambda x: x['lengthText']['simpleText'],