Introduce the Bluetooth transport layer

[dclause]

Description
Add support for a new Bluetooth transport layer to enable communication with remote boards/devices over Bluetooth.

Motivation
The current transport system does not support Bluetooth. Adding a Bluetooth layer will enable remote control and communication with Bluetooth-enabled devices, which is currently impossible with the existing setup.

Requirements

• Support for Arduino boards using the HC-05 Bluetooth module.
• Support for ESP32 boards with built-in Bluetooth capability.

Notes
Bluetooth acts as a virtual serial port. The implementation may consist of aliasing or reusing existing serial port abstractions with minimal changes.

API Changes
None. This feature adds an additional transport layer but does not modify existing APIs.