fix: 恢复腾讯云账单同步并完善成本预测

- 接入腾讯云单日账单、全局限频和指数退避

- 修正月末费用预测并增加账期提示和费用归因

- 补充腾讯云限频及账单归因回归测试

backend/cloud/billing.go

@@ -16,13 +16,16 @@ type BillingFetcher interface {
 	FetchDailyBill(billingDate string) ([]CloudBillingRecord, error)
 }
 
+// SupportedBillingProviders 已接入账单 API 的云厂商列表。 // Logan.Li
+var SupportedBillingProviders = []string{"aliyun", "tencent"}
+
 // NewBillingFetcher 根据云厂商创建账单拉取器
 func NewBillingFetcher(provider, accessKey, secretKey string) BillingFetcher {
 	switch provider {
 	case "aliyun":
-		if p := NewAliyunProvider(accessKey, secretKey); p != nil {
-			return p
-		}
+		return NewAliyunProvider(accessKey, secretKey)
+	case "tencent":
+		return NewTencentProvider(accessKey, secretKey)
 	}
 	return nil
-}
+}