timing: Use sub-second formatter for duration in table viewer

timing: Use sub-second formatter for duration in table viewer

A formatter makes the duration clearer, especially for large durations when
it's hard to figure the number of numbers in the string

Change-Id: I8b71ccc18c905809530df148d63881aced09c916
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/73802
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>