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`.

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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/core/info/room_version.rs

@@ -18,7 +18,7 @@ pub const STABLE_ROOM_VERSIONS: &[RoomVersionId] = &[
 
 /// Experimental, partially supported room versions
 pub const UNSTABLE_ROOM_VERSIONS: &[RoomVersionId] =
-	&[RoomVersionId::V3, RoomVersionId::V4, RoomVersionId::V5];
+	&[RoomVersionId::V3, RoomVersionId::V4, RoomVersionId::V5, RoomVersionId::V12];
 
 type RoomVersion = (RoomVersionId, RoomVersionStability);