Let runner subcycle

[uekerman]

Currently, subcycling is disabled by always doing the full time window:

fmi-runner/fmiprecice/runner.py

Lines 198 to 200 in 93d6c21

	# Compute current time step size
	precice_dt = participant.get_max_time_step_size()
	dt = precice_dt # FMU always does the max possible dt

How to enable it: https://precice.org/couple-your-code-time-step-sizes.html

Open question: From where do we get the FMU's dt? Is there a standard way how such things are modeled within an FMU, including adaptive time stepping? Fallback: we define a fixed dt in the configuration.