Bill a month of car park sessions with per-day caps across midnight, shop validations and a grace period

# Bill a month of car park sessions Inputs: `sessions.csv` (every entry/exit recorded by the barrier in October 2026, with whether a shop validated the ticket) and `tariff.json`. Charge each session: - Each calendar day a session touches is charged separately: the tariff's price per started hour on that day, capped at the tariff's daily cap for that day. A day piece runs from entry (or midnight) to exit (or midnight); a piece of 0 minutes costs nothing. - A validated session gets its first `validation_free_hours` hours free: take them off the first day's piece before counting started hours (any free time left over does not move to the next day). - A session shorter than `grace_minutes` minutes from entry to exit is free. - A started hour is any part of an hour: 61 minutes is 2 started hours, 60 minutes is 1. Write `out/parking.json`: `{"charges": {"<session_id>": <amount>, ...}, "by_plate": {"<plate>": <total for that plate>, ...}, "total": <sum of all charges>}` with every session listed (free ones as 0). ## 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.