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_mutex_test.go

@@ -0,0 +1,77 @@
+package channelserver
+
+import (
+	"testing"
+)
+
+// Test that all mutex handlers don't panic (they are empty implementations)
+
+func TestHandleMsgSysCreateMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysCreateMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysCreateMutex(session, nil)
+}
+
+func TestHandleMsgSysCreateOpenMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysCreateOpenMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysCreateOpenMutex(session, nil)
+}
+
+func TestHandleMsgSysDeleteMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysDeleteMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysDeleteMutex(session, nil)
+}
+
+func TestHandleMsgSysOpenMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysOpenMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysOpenMutex(session, nil)
+}
+
+func TestHandleMsgSysCloseMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysCloseMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysCloseMutex(session, nil)
+}