invite -> highlight count = 1.

AccountDataUpdate represents the (global) `account_data` section of a v2 sync response.

The purpose of global cache is to store global-level information about all rooms the server is aware of.

Subset of data from internal.RoomMetadata which we can glean from invite_state.

InviteUpdate corresponds to a key-value pair from a v2 sync's `invite` section.

RecieptUpdate corresponds to a receipt EDU in the `ephemeral` section of a joined room's v2 sync resposne.

RoomAccountDataUpdate represents the `account_data` section of joined room's v2 sync response.

RoomEventUpdate corresponds to a single event seen in a joined room's timeline under sync v2.

TypingEdu corresponds to a typing EDU in the `ephemeral` section of a joined room's v2 sync resposne.

UnreadCountUpdate represents a change in highlight or notification count change.

Tracks data specific to a given user.

UserRoomData describes a single room from the perspective of particular user.

Subset of store functions used by the user cache.