Keep the LRU order of CallbackDataCache when persisting it - #5397

With arbitrary_callback_data and a persistence, the keyboards that are used the most can be the first ones evicted from CallbackDataCache, so their buttons start returning InvalidCallbackData.

persistence_data builds its list from self._keyboard_data.values(). For a cachetools.LRUCache, that goes through __getitem__ for every key, which marks each keyboard as just used, in insertion order. Application.update_persistence reads this property on every run, so after each run the LRU order is simply "oldest keyboard first", regardless of how recently it was pressed. The same order is used when loading the data after a restart.

cdc = CallbackDataCache(bot, maxsize=2)
menu = ...  # keyboard sent first, pressed regularly
old = ...   # keyboard sent later, never pressed again
# press a button of `menu`
cdc.persistence_data             # what update_persistence does
cdc.process_keyboard(new_markup)  # evicts `menu` instead of `old`

Changes proposed in this pull request:

• Read the keyboards in persistence_data without updating the LRU order, and return them sorted by access_time (least recently used first).
• Insert the keyboards sorted by access_time in load_persistence_data, so the order after a restart matches the one before (also for data stored by earlier versions).
• Add a test that checks which keyboard is evicted after reading persistence_data, with and without reloading it.