thorium_actor: add thorium_actor_get_time_in_seconds()

Link: https://github.com/GeneAssembly/biosal/issues/803
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
unitig: add graph traversal speed in unitig visitor script

Link: https://github.com/GeneAssembly/biosal/issues/803
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>