Settle a wedding caterer's final headcount from changing replies, merged duplicate guests and birthdays on the day

# Work out the wedding caterer's final headcount and bill Inputs: `guests.csv` (guest_id, name, date_of_birth, merged_into), `rsvps.csv` (every reply received: guest_id, replied_at, attending, plus_one), `menu.json` (event date, prices, the child age limit and the service charge) and `planner-notes.txt`. Every amount is in pounds. The files are the record; where notes disagree with them, the files win. Rules: - A guest record with merged_into set is a duplicate: its replies count as replies of the guest it names, and it is never a guest in its own right. - Each guest's latest reply by actual time counts (replied_at carries a UTC offset; compare the moments, not the text). - A guest attends if their latest reply says attending yes; a guest with no reply does not attend. If that reply says plus_one yes, they bring one extra adult. - A guest is a child if they are under 12 on the event_date, worked out from the full date of birth (a guest whose 12th birthday is on the event_date is an adult). - Food cost = adults x adult_price + children x child_price (plus-ones count as adults). - Service charge = service_charge_pct of the food cost, rounded half-up to the penny. Write `out/catering.json`: `{"attending": [<sorted guest_ids attending>], "adults": <count incl. plus-ones>, "children": <count>, "food": <food cost>, "service_charge": <amount>, "total": <food + service charge>}`. ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.