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>