API: Use UserId from ruma-identifiers for stronger validation

The crate ruma-identifiers was updated to support
historical IDs, so it can be safely used now
2 jobs for roomid-userid-types in 28 minutes and 33 seconds
Status Job ID Name Coverage
  .Pre
passed #592004
flatpak

00:27:32

 
  Check
passed #592005
check

00:01:01