feat(cron): implement IP ban maintenance tasks

Add IPBanManager to handle periodic background jobs including:
- Expiring outdated bans
- Syncing hit counts from Redis to DB
- Performing full Redis state synchronization

Additionally, update the service expiration logic to use system time
and add unit tests for CIDR normalization and overlap checking.

internal/service/ip_ban.go

@@ -7,6 +7,7 @@ import (
 	"log/slog"
 	"net"
 	"strings"
+	"time"
 
 	"github.com/ez-api/ez-api/internal/model"
 	"github.com/redis/go-redis/v9"
@@ -288,12 +289,14 @@ func (s *IPBanService) SyncAllToRedis(ctx context.Context) error {
 
 // ExpireOutdatedBans marks expired bans and removes them from Redis.
 func (s *IPBanService) ExpireOutdatedBans(ctx context.Context) (int64, error) {
+	now := time.Now().Unix()
+
 	// Find active bans that have expired
 	var expiredBans []model.IPBan
 	if err := s.db.WithContext(ctx).
 		Where("status = ? AND expires_at IS NOT NULL AND expires_at <= ?",
 			model.IPBanStatusActive,
-			ctx.Value("now")). // This should be time.Now().Unix() in caller
+			now).
 		Find(&expiredBans).Error; err != nil {
 		return 0, err
 	}