Implement room v12 (#943)

**Does not yet work!** Currently, state resolution does not correctly resolve conflicting states. Everything else appears to work as expected, so stateres will be fixed soon, then we should be clear for takeoff.

Also: a lot of things currently accept a nullable room ID that really just don't need to. This will need tidying up before merge. Some authentication checks have also been disabled temporarily but nothing important.

A lot of things are tagged with `TODO(hydra)`, those need resolving before merge. External contributors should PR to the `hydra/public` branch, *not* ` main`.

---

This PR should be squash merged.

Reviewed-on: https://forgejo.ellis.link/continuwuation/continuwuity/pulls/943
Co-authored-by: nexy7574 <git@nexy7574.co.uk>
Co-committed-by: nexy7574 <git@nexy7574.co.uk>

src/service/rooms/auth_chain/mod.rs

@@ -195,13 +195,15 @@ async fn get_auth_chain_inner(
 				debug_error!(?event_id, ?e, "Could not find pdu mentioned in auth events");
 			},
 			| Ok(pdu) => {
-				if pdu.room_id != room_id {
-					return Err!(Request(Forbidden(error!(
-						?event_id,
-						?room_id,
-						wrong_room_id = ?pdu.room_id,
-						"auth event for incorrect room"
-					))));
+				if let Some(claimed_room_id) = pdu.room_id.clone() {
+					if claimed_room_id != *room_id {
+						return Err!(Request(Forbidden(error!(
+							?event_id,
+							?room_id,
+							wrong_room_id = ?pdu.room_id.unwrap(),
+							"auth event for incorrect room"
+						))));
+					}
 				}
 
 				for auth_event in &pdu.auth_events {