Improve CompatMgr behaviour for unknown versions

Improve CompatMgr behaviour for unknown versions

Currently, Impostor will show an "Client is in an invalid state."
message if a player tries to join a match where the host or the joining
player is using a version unknown to Impostor.

This message confused a *lot* of people, so this PR changes the API such
that if the version is not registered, the version itself is put in a
compatibility group and compared, assuming no other game versions are
compatible with it. This works fine in most cases, as Among Us network
versions generally increase over time.

Failure on 2222.2.2 (which is ancient at this point, so likely no longer
used) and future cases where Innersloth messes up (which is unlikely) is
an acceptable consequence to me.