refactor(backend): 添加 service 缓存端口

backend/internal/service/ports/billing_cache.go

@@ -0,0 +1,31 @@
+package ports
+
+import (
+	"context"
+	"time"
+)
+
+// SubscriptionCacheData represents cached subscription data
+type SubscriptionCacheData struct {
+	Status       string
+	ExpiresAt    time.Time
+	DailyUsage   float64
+	WeeklyUsage  float64
+	MonthlyUsage float64
+	Version      int64
+}
+
+// BillingCache defines cache operations for billing service
+type BillingCache interface {
+	// Balance operations
+	GetUserBalance(ctx context.Context, userID int64) (float64, error)
+	SetUserBalance(ctx context.Context, userID int64, balance float64) error
+	DeductUserBalance(ctx context.Context, userID int64, amount float64) error
+	InvalidateUserBalance(ctx context.Context, userID int64) error
+
+	// Subscription operations
+	GetSubscriptionCache(ctx context.Context, userID, groupID int64) (*SubscriptionCacheData, error)
+	SetSubscriptionCache(ctx context.Context, userID, groupID int64, data *SubscriptionCacheData) error
+	UpdateSubscriptionUsage(ctx context.Context, userID, groupID int64, cost float64) error
+	InvalidateSubscriptionCache(ctx context.Context, userID, groupID int64) error
+}