refactor: Promote handling unsigned data out of timeline

Also fixes:
- Transaction IDs leaking in event route
- Age not being set for event relations or threads
- Both of the above for search results

Notes down concern with relations table

src/api/client/threads.rs

@@ -28,6 +28,9 @@ pub(crate) async fn get_threads_route(
 		.transpose()?
 		.unwrap_or_else(PduCount::max);
 
+	// TODO: bundled aggregation
+	// TODO: user_can_see_event and set_unsigned should be at the same level /
+	// function, so unsigned is only set for seen events.
 	let threads: Vec<(PduCount, PduEvent)> = services
 		.rooms
 		.threads