Creates transmissions and observations tables from existing packets table.
- Groups packets by hash → 1 transmission per unique hash
- Creates 1 observation per original packet row with FK to transmission
- Idempotent: drops and recreates new tables on each run
- Does NOT modify the original packets table
- Prints stats and verifies counts match
Tested on test DB: 33813 packets → 11530 transmissions (2.93x dedup ratio)