thorium: use static keyword in worker pool

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use the static keyword in actor and worker_pool

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use static functions in worker

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
performance: use static keyword in latency_probe

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