test: expand channelserver coverage from 16% to 20%

Add comprehensive tests for handler functions and utilities:
- Achievement system (GetAchData, curves, mappings)
- Language system (getLangStrings)
- Core handlers (empty handlers, simple responses)
- Cafe/boost handlers
- Diva defense handlers
- Reward, caravan, tactics handlers
- Festa/ranking handlers
- Cast binary constants

server/channelserver/handlers_festa_test.go

@@ -0,0 +1,112 @@
+package channelserver
+
+import (
+	"testing"
+
+	"erupe-ce/config"
+	"erupe-ce/network/mhfpacket"
+)
+
+func TestHandleMsgMhfEnumerateRanking_Default(t *testing.T) {
+	server := createMockServer()
+	server.erupeConfig = &config.Config{
+		DevMode: true,
+		DevModeOptions: config.DevModeOptions{
+			TournamentEvent: 0, // Default state
+		},
+	}
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfEnumerateRanking{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfEnumerateRanking(session, pkt)
+
+	select {
+	case p := <-session.sendPackets:
+		if len(p.data) == 0 {
+			t.Error("Response packet should have data")
+		}
+	default:
+		t.Error("No response packet queued")
+	}
+}
+
+func TestHandleMsgMhfEnumerateRanking_State1(t *testing.T) {
+	server := createMockServer()
+	server.erupeConfig = &config.Config{
+		DevMode: true,
+		DevModeOptions: config.DevModeOptions{
+			TournamentEvent: 1,
+		},
+	}
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfEnumerateRanking{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfEnumerateRanking(session, pkt)
+
+	select {
+	case p := <-session.sendPackets:
+		if len(p.data) == 0 {
+			t.Error("Response packet should have data")
+		}
+	default:
+		t.Error("No response packet queued")
+	}
+}
+
+func TestHandleMsgMhfEnumerateRanking_State2(t *testing.T) {
+	server := createMockServer()
+	server.erupeConfig = &config.Config{
+		DevMode: true,
+		DevModeOptions: config.DevModeOptions{
+			TournamentEvent: 2,
+		},
+	}
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfEnumerateRanking{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfEnumerateRanking(session, pkt)
+
+	select {
+	case p := <-session.sendPackets:
+		if len(p.data) == 0 {
+			t.Error("Response packet should have data")
+		}
+	default:
+		t.Error("No response packet queued")
+	}
+}
+
+func TestHandleMsgMhfEnumerateRanking_State3(t *testing.T) {
+	server := createMockServer()
+	server.erupeConfig = &config.Config{
+		DevMode: true,
+		DevModeOptions: config.DevModeOptions{
+			TournamentEvent: 3,
+		},
+	}
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfEnumerateRanking{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfEnumerateRanking(session, pkt)
+
+	select {
+	case p := <-session.sendPackets:
+		if len(p.data) == 0 {
+			t.Error("Response packet should have data")
+		}
+	default:
+		t.Error("No response packet queued")
+	}
+}