thorium: add thorium_worker_allocate

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: add zero-copy code path for send

Link: https://github.com/GeneAssembly/biosal/issues/705
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use zero-copy send to send vector

Link: https://github.com/GeneAssembly/biosal/issues/704
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>