bug fixes: jazzy: serial transport

[kristkis]

Summary

Fix serial transport build failure on Zephyr 4.1+ and make the UART device configurable without patching module source files.

• Build fix: <unistd.h> / <zephyr/posix/unistd.h> cause _SC_ADVISORY_INFO enum/macro collision on Zephyr 4.1 with SDK 0.17.0. Replaced with standard C headers + k_usleep().
• Configurable UART: UART device is now selectable via DT alias microros-serial in the application's board overlay. Falls back to usart1 when the alias is absent (no breaking change).
• Bug fixes: ring_buf_init() was using the wrong buffer, device_is_ready() replaces a null-pointer check that can't trigger in modern Zephyr, dead code removed.

Motivation

Anyone using the serial transport on Zephyr 4.1+ with the Zephyr SDK 0.17.0 ARM toolchain hits a hard build error:

zephyr/posix/sys/sysconf.h:17:9: error: expected identifier before numeric constant 17 | _SC_ADVISORY_INFO

This is caused by <unistd.h> pulling in the toolchain's POSIX sysconf macros, which collide with Zephyr's own POSIX enum of the same names. The only symbols actually needed from <unistd.h> were size_t, bool, and usleep() — the first two come from standard C headers, and usleep() is replaced by k_usleep().
Additionally, UART_NODE was hardcoded to DT_NODELABEL(usart1), forcing anyone with a different UART (e.g. lpuart1 on STM32G4) to patch this file locally. The DT alias approach lets applications select the UART in their overlay:

/ { aliases { microros-serial = &lpuart1; }; };

Discussion point: DT alias vs Kconfig for UART selection

This PR uses a DT alias (microros-serial) for UART selection because it follows Zephyr idiom (similar to zephyr,console) and works cleanly with the devicetree preprocessor. A Kconfig string approach was considered but Kconfig strings expand as quoted C strings, which are incompatible with DT_NODELABEL() token pasting.
Open to feedback on whether a different mechanism (e.g. DT chosen node, or a Kconfig that selects between a fixed set of UART labels) would be preferred by the maintainers.

Changes

File	Change
microros_transports.h	<unistd.h> → <stddef.h> / <stdint.h> / <stdbool.h>
microros_transports.c	Remove <zephyr/posix/unistd.h>, usleep() → k_usleep()
microros_transports.c	Configurable UART via DT_ALIAS(microros_serial), fallback to usart1
microros_transports.c	Fix ring_buf_init() using wrong buffer (uart_out_buffer → uart_in_buffer)
microros_transports.c	Remove unused uart_out_buffer and out_ringbuf
microros_transports.c	device_is_ready() instead of null check in transport_open()

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com