unitig: reduce visitor count per worker to 100

Link: https://github.com/GeneAssembly/biosal/issues/804
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
tests: convert time from the format 0m0.012s to a number of seconds

Link: https://github.com/GeneAssembly/biosal/issues/802
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
tests: change invalid time values to 0 seconds

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
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>