feat: Refactor CLI API client by splitting billing, carrier, and charging modules into separate files

- Extract Invoice, Payment, Subscriber types and GetInvoices, GetPayments, GenerateInvoice methods to billing.go
- Extract CarrierInfo, ConnectivityStatus, ProfileInfo types and carrier connector methods to carrier.go
- Extract CreditCheckRequest/Response, CreditBalanceResponse types and charging engine methods to charging.go
- Add PacketStats, CreditInfo types and GetPacketStats, GetCreditInfo

apps/cli/internal/api/charging.go

@@ -0,0 +1,64 @@
+package api
+
+// Charging Engine Integration
+type CreditCheckRequest struct {
+	BytesRequested uint64 `json:"bytes_requested"`
+}
+
+type CreditCheckResponse struct {
+	Allowed   bool   `json:"allowed"`
+	Available uint64 `json:"available"`
+	Requested uint64 `json:"requested"`
+	Remaining uint64 `json:"remaining"`
+}
+
+type CreditBalanceResponse struct {
+	Balance uint64 `json:"balance"`
+}
+
+type CreditAddRequest struct {
+	BytesToAdd uint64 `json:"bytes_to_add"`
+}
+
+type CreditDeductRequest struct {
+	BytesUsed uint64 `json:"bytes_used"`
+}
+
+// CheckCredit checks if a subscriber has enough credit
+func (c *Client) CheckCredit(ip string, bytesRequested uint64) (*CreditCheckResponse, error) {
+	var resp CreditCheckResponse
+	req := CreditCheckRequest{BytesRequested: bytesRequested}
+	if err := c.doPostJSON("/v1/charging/credit/"+ip+"/check", req, &resp); err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}
+
+// GetBalance gets the current credit balance for a subscriber
+func (c *Client) GetBalance(ip string) (*CreditBalanceResponse, error) {
+	var resp CreditBalanceResponse
+	if err := c.doGetJSON("/v1/charging/credit/"+ip+"/balance", &resp); err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}
+
+// AddCredit adds credit to a subscriber
+func (c *Client) AddCredit(ip string, bytesToAdd uint64) (*CreditBalanceResponse, error) {
+	var resp CreditBalanceResponse
+	req := CreditAddRequest{BytesToAdd: bytesToAdd}
+	if err := c.doPostJSON("/v1/charging/credit/"+ip+"/add", req, &resp); err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}
+
+// DeductCredit deducts credit from a subscriber
+func (c *Client) DeductCredit(ip string, bytesUsed uint64) (*CreditBalanceResponse, error) {
+	var resp CreditBalanceResponse
+	req := CreditDeductRequest{BytesUsed: bytesUsed}
+	if err := c.doPostJSON("/v1/charging/credit/"+ip+"/deduct", req, &resp); err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}