Set baudrate, add mock serial struct to test with.

Sources/SwiftRPLidar/LidarSerial.swift

@@ -7,4 +7,5 @@ public protocol LidarSerial {
     func openPort() throws;
     func readData(ofLength: Int) throws -> Data;
     func writeData(_ data: Data) throws -> Int;
+    func setBaudrate(baudrate: Int)
 }

Sources/SwiftRPLidar/SwiftRPLidar.swift

@@ -78,6 +78,7 @@ public class SwiftRPLidar {
     public func connect() throws {
         disconnect()
         try serialPort!.openPort()
+        serialPort?.setBaudrate(baudrate: 115200)
     }
     
     public func disconnect(){