- Add minecraft-data for 1.12.2 (protocol 340)
- Generate proto_generated/v1_12_2
- Add v1_12_2 legacy handlers to client.Login (OnDisconnect,
OnCompress, OnSuccess) and client.Status (OnStatus, OnPong)
- Same pattern as v1_8: RegisterUntilLatest only registers
upward, so legacy versions need explicit RegisterCritical handlers