* WIP Event rejection
* Still send back errors for rejected events
Instead, discard them at the federationapi /send layer rather than
re-implementing checks at the clientapi/PerformJoin layer.
* Implement rejected events
Critically, rejected events CAN cause state resolution to happen
as it can merge forks in the DAG. This is fine, _provided_ we
do not add the rejected event when performing state resolution,
which is what this PR does. It also fixes the error handling
when NotAllowed happens, as we were checking too early and needlessly
handling NotAllowed in more than one place.
* Update test to match reality
* Modify InputRoomEvents to no longer return an error
Errors do not serialise across HTTP boundaries in polylith mode,
so instead set fields on the InputRoomEventsResponse. Add `Err()`
function to make the API shape basically the same.
* Remove redundant returns; linting
* Update blacklist
* Initial FIFOing of roomserver inputs
* Remove EventID response from api.InputRoomEventsResponse
* Don't send back event ID unnecessarily
* Fix ordering hopefully
* Reduce copies, use buffered task channel to reduce contention on other rooms
* Fix error handling
* Add Queryer and use embedded structs
* Add Inputer and factor out more RS API stuff
This neatly splits up the RS API based on the functionality it provides,
whilst providing a useful place for code sharing via the `helpers` package.
