feat(rcs): migrate all RCS APIs from rainyun-go-sdk

- 35 endpoints across 14 files, response structs split for reuse
- Reuse RcsRecord/Node/Plan/OsInfo/UsageData across list/detail/create
- Fix source bugs: {id} path placeholders, missing / in firewall pos path,
  missing body in ChargeRcsTrafic, resp vs &resp
- Add HTTPMethod_PATCH, common.BasicOperationResponse, VncConnectionInfo

apis/rcs/upgrade.go

@@ -0,0 +1,21 @@
+package rcs
+
+import (
+	"fmt"
+
+	"github.com/XingfenD/rainyun_api_go_sdk/apis/common"
+	"github.com/XingfenD/rainyun_api_go_sdk/constant"
+)
+
+type UpgradeRcsRequest struct {
+	DestPlan     int `json:"dest_plan"`      // 升级到的套餐ID
+	WithCouponID int `json:"with_coupon_id"` // 优惠券ID,默认为0
+}
+
+func (s *RcsService) UpgradeRcs(id, plan, coupon int) (*common.BasicOperationResponse, error) {
+	path := fmt.Sprintf("/product/rcs/%d/upgrade", id)
+
+	var resp common.BasicOperationResponse
+	err := s.client.Do(constant.HTTPMethod_POST, path, nil, UpgradeRcsRequest{DestPlan: plan, WithCouponID: coupon}, &resp)
+	return &resp, err
+}