Make the sleep time in isCmdEmpty() of FelixTxCore configurable
For FELIX test setups which do not have other hidden latencies in the DAQ chain, should we make the sleep time
in isCmdEmpty() here a configurable parameter from the controller config? Analogous to the flushWaitTime parameter here for FelixRxCore.
This will enable faster configuration for multi-chip or multi-module tests, until we can get rid of this manual wait time while flushing the buffers completely. This can be possible once the flush method of send_data() in felix-star becomes completely blocking with a user callback to check on the status.