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_register_test.go

@@ -0,0 +1,63 @@
+package channelserver
+
+import (
+	"testing"
+)
+
+func TestHandleMsgSysNotifyRegister(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysNotifyRegister panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysNotifyRegister(session, nil)
+}
+
+func TestGetRaviSemaphore_None(t *testing.T) {
+	server := createMockServer()
+	server.semaphore = make(map[string]*Semaphore)
+
+	result := getRaviSemaphore(server)
+
+	if result != nil {
+		t.Error("Expected nil when no raviente semaphore exists")
+	}
+}
+
+func TestGetRaviSemaphore_Found(t *testing.T) {
+	server := createMockServer()
+	server.semaphore = make(map[string]*Semaphore)
+
+	// Create a raviente semaphore (matches prefix hs_l0u3B5 and suffix 3)
+	sema := NewSemaphore(server, "hs_l0u3B53", 32)
+	server.semaphore["hs_l0u3B53"] = sema
+
+	result := getRaviSemaphore(server)
+
+	if result == nil {
+		t.Error("Expected to find raviente semaphore")
+	}
+	if result.id_semaphore != "hs_l0u3B53" {
+		t.Errorf("Wrong semaphore returned: %s", result.id_semaphore)
+	}
+}
+
+func TestGetRaviSemaphore_WrongSuffix(t *testing.T) {
+	server := createMockServer()
+	server.semaphore = make(map[string]*Semaphore)
+
+	// Create a semaphore with wrong suffix
+	sema := NewSemaphore(server, "hs_l0u3B51", 32)
+	server.semaphore["hs_l0u3B51"] = sema
+
+	result := getRaviSemaphore(server)
+
+	if result != nil {
+		t.Error("Should not match semaphore with wrong suffix")
+	}
+}