Hashed trace user events should do an all-reduce at the end instead of sending pt2pts to rank 0 during the run

[lifflander]

Describe the bug
When using trace::TraceScopedEventHash scope("XXX");, the node that calls this immediately sends a message to rank 0 with the hashed event, causing tons of messages that interfere with the application run. We should all-reduce these at the end of the run when we need to write out the STS file.