[ie/youtube] Add a PO Token Provider Framework (#12840)

https://github.com/yt-dlp/yt-dlp/tree/master/yt_dlp/extractor/youtube/pot/README.md

Authored by: coletdjnz

yt_dlp/YoutubeDL.py

@@ -640,6 +640,7 @@ class YoutubeDL:
         self._printed_messages = set()
         self._first_webpage_request = True
         self._post_hooks = []
+        self._close_hooks = []
         self._progress_hooks = []
         self._postprocessor_hooks = []
         self._download_retcode = 0
@@ -908,6 +909,11 @@ class YoutubeDL:
         """Add the post hook"""
         self._post_hooks.append(ph)
 
+    def add_close_hook(self, ch):
+        """Add a close hook, called when YoutubeDL.close() is called"""
+        assert callable(ch), 'Close hook must be callable'
+        self._close_hooks.append(ch)
+
     def add_progress_hook(self, ph):
         """Add the download progress hook"""
         self._progress_hooks.append(ph)
@@ -1016,6 +1022,9 @@ class YoutubeDL:
             self._request_director.close()
             del self._request_director
 
+        for close_hook in self._close_hooks:
+            close_hook()
+
     def trouble(self, message=None, tb=None, is_error=True):
         """Determine action to take when a download problem appears.