Add Raspberry Pi Pico port (#1232)

* Add Raspberry Pi Pico port
- Adds BACnet/IP with abstracted network layer
- Adds BACnet MS/TP support using RS485/UART
- Includes README with examples

* Add Pico 2 MS/TP demo, CI, and docs

ports/pico/rs485.h

@@ -0,0 +1,52 @@
+/**************************************************************************
+ *
+ * Copyright (C) 2025 Testimony Adams <adamstestimony@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later WITH GCC-exception-2.0
+ *
+ *********************************************************************/
+
+#ifndef RS485_H
+#define RS485_H
+
+#include <stdint.h>
+#include <stdbool.h>
+#include "pico/stdlib.h"
+#include "hardware/uart.h"
+#include "hardware/gpio.h"
+#include "hardware/regs/uart.h"
+
+#define RS485_UART_ID uart1
+#define RS485_BAUD_RATE 38400
+#define RS485_TX_PIN 8
+#define RS485_RX_PIN 9
+#define RS485_DE_PIN 10
+#define DATA_BIT 8
+#define STOP_BIT 1
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+void rs485_rts_enable(bool enable);
+bool rs485_rts_enabled(void);
+bool rs485_byte_available(uint8_t *data_register);
+bool rs485_receive_error(void);
+
+void rs485_bytes_send(const uint8_t *buffer, uint16_t nbytes);
+
+uint32_t rs485_baud_rate(void);
+bool rs485_baud_rate_set(uint32_t baud);
+
+uint32_t rs485_silence_milliseconds(void);
+void rs485_silence_reset(void);
+
+uint32_t rs485_bytes_transmitted(void);
+uint32_t rs485_bytes_received(void);
+
+void rs485_init(void);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+#endif