test: expand channelserver coverage from 20% to 25%

Add tests for:
- Discord handlers (getPlayerSlice, getCharacterList)
- House handlers (boxToBytes, HouseData, Title structs)
- Mail struct tests
- Mercenary handlers (Partner, HunterNavi structs)
- Shop/Gacha handlers (writeShopItems, ShopItem, Gacha structs)
- Additional handler coverage for guild, tower, and simple handlers
- Stage handler tests for binary operations and enumeration
- Channel server tests for BroadcastMHF and session management

server/channelserver/handlers_rengoku_test.go

@@ -26,3 +26,28 @@ func TestHandleMsgMhfGetRengokuRankingRank(t *testing.T) {
 		t.Error("No response packet queued")
 	}
 }
+
+func TestRengokuScoreStruct(t *testing.T) {
+	score := RengokuScore{
+		Name:  "TestPlayer",
+		Score: 12345,
+	}
+
+	if score.Name != "TestPlayer" {
+		t.Errorf("Name = %s, want TestPlayer", score.Name)
+	}
+	if score.Score != 12345 {
+		t.Errorf("Score = %d, want 12345", score.Score)
+	}
+}
+
+func TestRengokuScoreStruct_DefaultValues(t *testing.T) {
+	score := RengokuScore{}
+
+	if score.Name != "" {
+		t.Errorf("Default Name should be empty, got %s", score.Name)
+	}
+	if score.Score != 0 {
+		t.Errorf("Default Score should be 0, got %d", score.Score)
+	}
+}