refactor(client): wrap all external requests in retry transport

backend/cmd/api/main.go

@@ -38,7 +38,11 @@ func run(logger *slog.Logger) error {
 		return fmt.Errorf("load configuration: %w", err)
 	}
 
-	httpClient := &http.Client{Timeout: config.ZarinHubTimeout}
+	httpClient := zarinhub.NewHTTPClient(
+		config.ZarinHubTimeout,
+		config.ZarinHubRetries,
+		logger,
+	)
 	tokenManager := zarinhub.NewTokenManager(
 		httpClient,
 		config.ZarinHubAuthEndpoint,
@@ -46,9 +50,10 @@ func run(logger *slog.Logger) error {
 		config.ZarinHubPassword,
 	)
 
+	authTimeout := time.Duration(config.ZarinHubRetries+1)*config.ZarinHubTimeout + 10*time.Second
 	authContext, cancelAuth := context.WithTimeout(
 		context.Background(),
-		config.ZarinHubTimeout,
+		authTimeout,
 	)
 	_, err = tokenManager.AccessToken(authContext)
 	cancelAuth()