Currently, this is something that's missing even in clients like Element
(!?!) I will sometimes miss when invites are sent - like when I'm
sleeping - and then when I start back up NeoChat I have no idea when
they tried to invite me. This can get worse on bigger timescales, like
when you go on vacation for a few days.
This is only called after we already get an event with lastEvent() so
doing it again is useless. Instead, we should refactor it to behave like
similar functions (e.g. isEventHighlighted.)