realtime_helpers.cpp has option to only used sched_fifo

[nsk126]

Currently, realtime_helpers.cpp offers configure_sched_fifo to set thread priority. however, the function sets the policy to SCHED_FIFO. In a PREEMPT_RT kernel, where multiple threads could have RT priority, SCHED_FIFO threads may not rotate. A SCHED_RR policy may be better.

realtime_tools/realtime_tools/src/realtime_helpers.cpp

Lines 74 to 99 in e668fb5

	bool configure_sched_fifo(int priority)
	{
	#ifdef _WIN32
	HANDLE thread = GetCurrentThread();
	return SetThreadPriority(thread, priority);
	#elif defined(__APPLE__)
	// macOS implementation using pthread_setschedparam with SCHED_FIFO
	pthread_t thread = pthread_self();
	struct sched_param schedp;
	memset(&schedp, 0, sizeof(schedp));
	schedp.sched_priority = priority;
	int policy = SCHED_FIFO;
	if (pthread_setschedparam(thread, policy, &schedp) == 0) {
	return true;
	} else {
	// Optionally log strerror(errno) for debugging
	return false;
	}
	#else
	struct sched_param schedp;
	memset(&schedp, 0, sizeof(schedp));
	schedp.sched_priority = priority;
	return !sched_setscheduler(0, SCHED_FIFO, &schedp);
	#endif
	}

I've started to use realtime_helpers.cpp in ros2control hardware interfaces and think it would be better if there was an option to opt for another policy i.e SCHED_RR.

I propose adding a new configure_sched_rr function that uses the SCHED_RR policy.

https://stackoverflow.com/questions/9392415/linux-sched-other-sched-fifo-and-sched-rr-differences
https://man7.org/linux/man-pages/man7/sched.7.html