Check overhead of breadcrumb
I noticed here https://xgitlab.cels.anl.gov/sds/margo/blob/master/src/margo.c#L1249 that the breadcrumb mechanism requires converting an address into a string and hashing this string within the margo_forward path, which may add significant overhead in RPC. This overhead would need to be checked and, if necessary, an alternate mechanism should be put in place (or we should be able to disable breadcrumbs).