Begin reworking update handling

Use a fixed-size queue instead of a callback to deal with updates.

Port the message box and entity cache from grammers to start off
with a clean design.

Temporarily get rid of other cruft such as automatic pings or old
catch up implementation.

telethon/_client/telegramclient.py

@@ -2665,6 +2665,7 @@ class TelegramClient:
             flood_sleep_threshold: int = 60,
             # Update handling.
             receive_updates: bool = True,
+            max_queued_updates: int = 100,
     ):
         telegrambaseclient.init(**locals())
 
@@ -3509,10 +3510,6 @@ class TelegramClient:
     async def _clean_exported_senders(self: 'TelegramClient'):
         pass
 
-    @forward_call(updates._handle_update)
-    def _handle_update(self: 'TelegramClient', update):
-        pass
-
     @forward_call(auth._update_session_state)
     async def _update_session_state(self, user, *, save=True):
         pass