test: increase total coverage from 31.3% to 40.7%

Add batch Parse/Build tests for ~150 mhfpacket types, net.Pipe-based
round-trip tests for CryptConn Send/ReadPacket, overflow panic tests
for all byteframe Read types, and additional empty handler coverage.

server/channelserver/handlers_simple_test.go

@@ -298,6 +298,10 @@ func TestEmptyHandlers_NoDb(t *testing.T) {
 		{"handleMsgMhfStampcardPrize", handleMsgMhfStampcardPrize},
 		{"handleMsgMhfUnreserveSrg", handleMsgMhfUnreserveSrg},
 		{"handleMsgMhfKickExportForce", handleMsgMhfKickExportForce},
+		{"handleMsgSysSetStatus", handleMsgSysSetStatus},
+		{"handleMsgSysEcho", handleMsgSysEcho},
+		{"handleMsgMhfUseUdShopCoin", handleMsgMhfUseUdShopCoin},
+		{"handleMsgMhfEnterTournamentQuest", handleMsgMhfEnterTournamentQuest},
 	}
 
 	for _, tt := range tests {