Add methods to set serial parameters and control lines in UsbSerialPort

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

lib/src/usb_serial_port.dart

@@ -32,6 +32,50 @@ class UsbSerialPort {
     return written ?? 0;
   }
 
+  /// Updates serial line parameters for an already-open port.
+  Future<void> setParameters({
+    required int baudRate,
+    int dataBits = 8,
+    UsbSerialParity parity = UsbSerialParity.none,
+    UsbSerialStopBits stopBits = UsbSerialStopBits.one,
+  }) async {
+    await _methods.invokeMethod<void>('setParameters', {
+      'portId': _portId,
+      'baudRate': baudRate,
+      'dataBits': dataBits,
+      'parity': parity.index,
+      'stopBits': FlutterUsbSerial._stopBitsIndex(stopBits),
+    });
+  }
+
+  /// Sets the DTR modem control line.
+  Future<void> setDTR(bool value) async {
+    await _methods.invokeMethod<void>('setDTR', {
+      'portId': _portId,
+      'value': value,
+    });
+  }
+
+  /// Sets the RTS modem control line.
+  Future<void> setRTS(bool value) async {
+    await _methods.invokeMethod<void>('setRTS', {
+      'portId': _portId,
+      'value': value,
+    });
+  }
+
+  /// Purges USB serial driver buffers when the driver supports it.
+  Future<void> purgeHwBuffers({
+    bool purgeWriteBuffers = true,
+    bool purgeReadBuffers = true,
+  }) async {
+    await _methods.invokeMethod<void>('purgeHwBuffers', {
+      'portId': _portId,
+      'purgeWriteBuffers': purgeWriteBuffers,
+      'purgeReadBuffers': purgeReadBuffers,
+    });
+  }
+
   /// Close the port and release native resources.
   Future<void> close() async {
     await _methods.invokeMethod<void>('close', {'portId': _portId});