Fix Teensy 4.x compilation error by updating HardwareSerial to Hardwa…

[mukptl]

…reSerialIMXRT (Teensyduino 1.59+)

Fix Teensy 4.x Compilation Error (HardwareSerial issue)

Problem

Compilation fails on newer Teensyduino (1.59+) with:
'class HardwareSerial' has no member named 'addMemoryForRead'

Cause

Teensyduino moved addMemoryForRead() from HardwareSerial to HardwareSerialIMXRT (Teensy 4.x specific).

Fix

Updated serial object types to HardwareSerialIMXRT in:

• AIO_v4_Firmware
• AIO_v4_Firmware_Keya_CANBUS_HPR_Dual_27.04.2025

Tested On

• Teensy 4.1
• Teensyduino 1.59+

Result

• Compilation successful
• Serial buffer functions working correctly

[mukptl]

Tested on Teensy 4.1 with Teensyduino 1.59+.
Fix resolves compilation error and restores addMemoryForRead functionality.