Charge daily late-payment interest and fixed compensation on overdue business invoices with part payments and credit notes

# Charge statutory interest and fixed compensation on late invoices Inputs: `invoices.csv` (every invoice issued to business customers, with issue and due dates), `payments.csv`, `credit-notes.csv` and `terms.json` (the annual interest rate, the statement date and the fixed-compensation bands). Work out the late-payment charges as at the statement date: - Interest runs on each day from the day after the due date up to and including the statement date, or up to and including the day the invoice was paid in full if that is earlier. - Each day's interest = outstanding principal x annual rate / 365. A payment reduces the principal from the day after it is received. - A credit note reduces the invoice amount from the start, as if that part had never been billed, whatever its date. - Fixed compensation: one fee per invoice that was paid in full after its due date or is still unpaid after it, chosen by the invoice amount after credit notes from the `fixed_fees` bands (the first band whose `below` is greater than that amount; `null` means no upper limit). - Round each invoice's interest to the cent half-up; totals are sums of the rounded figures. Write `out/late-charges.json`: `{"interest": {"<invoice_id>": <interest>, ...}, "fees": {"<invoice_id>": <fee>, ...}, "total_interest": <...>, "total_fees": <...>}`. List only invoices that have at least one day of interest, in both maps. ## 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.