Change get_pos_of_last_change to return upper bound

Enable state caches on workers

Use stream_change cache to make get_forward_extremeties_for_room cache more effective

Add cache to get_forward_extremeties_for_room

Ensure we don't mutate the cache of push rules

Add pagination support to publicRooms

Ensure we don't mutate state cache entries

Split out public room list into a worker process

make device IDs more useful for human disambiguation

Fix typo "persiting"

Limit how often we ask for keys from dead servers