test: expand channelserver coverage from 12% to 16%

Add comprehensive tests for handler files:
- handlers_object: object creation, positioning, binary ops
- handlers_semaphore: create, acquire, release, check, delete
- handlers_reserve: stub handlers and reserve188/18B
- handlers_event: registration, release, feature weapons
- handlers_mutex: create, open, close, delete operations
- handlers_campaign: enumerate, state, apply
- handlers_bbs: user status, SNS status, article apply
- handlers_tournament: info, entry, acquire
- handlers_users: user binary operations
- handlers_clients: client enumeration
- handlers_rengoku: ranking
- handlers_register: raviente semaphore functions
- handlers_tower: tower info, tenrouirai, seibatu ranking

All tests pass with race detection enabled.

server/channelserver/handlers_campaign_test.go

@@ -0,0 +1,70 @@
+package channelserver
+
+import (
+	"testing"
+
+	"erupe-ce/network/mhfpacket"
+)
+
+func TestHandleMsgMhfEnumerateCampaign(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfEnumerateCampaign{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfEnumerateCampaign(session, pkt)
+
+	// Verify response packet was queued (fail response expected)
+	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 TestHandleMsgMhfStateCampaign(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfStateCampaign{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfStateCampaign(session, pkt)
+
+	// Verify response packet was queued (fail response expected)
+	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 TestHandleMsgMhfApplyCampaign(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfApplyCampaign{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfApplyCampaign(session, pkt)
+
+	// Verify response packet was queued (fail response expected)
+	select {
+	case p := <-session.sendPackets:
+		if len(p.data) == 0 {
+			t.Error("Response packet should have data")
+		}
+	default:
+		t.Error("No response packet queued")
+	}
+}