Add serial configuration support to Gateway Modbus

- Introduced GatewayModbusSerialConfig structure to encapsulate serial communication settings.
- Added clamping functions for integer and size values to ensure valid configuration ranges.
- Updated GatewayModbusConfigFromValue to parse serial configuration from JSON input.
- Implemented transport type checking functions for TCP, RTU, ASCII, and Serial.
- Enhanced GatewayModbusConfigToValue to include serial configuration in output.

Signed-off-by: Tony <tonylu@tony-cloud.com>

components/gateway_modbus/include/gateway_modbus.hpp

@@ -18,14 +18,43 @@ constexpr uint16_t kGatewayModbusMaxReadBits = 2000;
 constexpr uint16_t kGatewayModbusMaxReadRegisters = 125;
 constexpr uint16_t kGatewayModbusMaxWriteBits = 1968;
 constexpr uint16_t kGatewayModbusMaxWriteRegisters = 123;
+constexpr uint32_t kGatewayModbusDefaultSerialBaudrate = 9600;
+constexpr uint32_t kGatewayModbusDefaultSerialResponseTimeoutMs = 20;
+constexpr uint32_t kGatewayModbusDefaultSerialInterFrameGapUs = 4000;
+
+struct GatewayModbusRs485Config {
+  bool enabled{false};
+  int de_pin{-1};
+};
+
+struct GatewayModbusSerialConfig {
+  int uart_port{1};
+  int tx_pin{-1};
+  int rx_pin{-1};
+  uint32_t baudrate{kGatewayModbusDefaultSerialBaudrate};
+  int data_bits{8};
+  std::string parity{"none"};
+  int stop_bits{1};
+  size_t rx_buffer_size{512};
+  size_t tx_buffer_size{512};
+  uint32_t response_timeout_ms{kGatewayModbusDefaultSerialResponseTimeoutMs};
+  uint32_t inter_frame_gap_us{kGatewayModbusDefaultSerialInterFrameGapUs};
+  GatewayModbusRs485Config rs485;
+};
 
 struct GatewayModbusConfig {
   std::string transport{"tcp-server"};
   std::string host;
   uint16_t port{kGatewayModbusDefaultTcpPort};
   uint8_t unit_id{1};
+  GatewayModbusSerialConfig serial;
 };
 
+bool GatewayModbusTransportIsTcp(const std::string& transport);
+bool GatewayModbusTransportIsRtu(const std::string& transport);
+bool GatewayModbusTransportIsAscii(const std::string& transport);
+bool GatewayModbusTransportIsSerial(const std::string& transport);
+
 enum class GatewayModbusSpace : uint8_t {
   kCoil = 1,
   kDiscreteInput = 2,