thorium_node: use double precision to get the throughput

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium_node: use 64-bit integers for counters to avoid overflow

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium_node: use a 64-bit integer for the tick number

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