Fix missing dedup in direct_forward and use atomic has_seen check

[ViezeVingertjes]

Added a few improvements to prevent packets from being repeated multiple times.

Fixes #57

[rightup]

Good catch on the missing dedup in direct_forward() - I've applied that fix separately.

One note: in trace.py the final else: will log "Duplicate packet, ignoring" for any unmatched condition. Should probably keep the specific duplicate check there or adjust the log message.

The refactor to match the C++ atomic hasSeen() pattern looks good. I need to test and digest it.