arecord: use better time granularity mili/micro/nanoseconds for split file names

[kfilipan]

This is more of a feature request rather than an issue. When using arecord with --max-file-time and --use-strftime, one cannot get nanoseconds in the file name. This is however available in the e.g. date command date +"%Y-%m-%d_%H-%M-%S.%N" (%N gives nanoseconds). This would be useful for testing sound card recording time delays because having only seconds is not precise enough, e.g. it could take days or weeks for even slightly better sound cards to experience a second of delay. Thank you!