Calendar: book slots in a 24-hour day, then times of day, cancelling and free slots

Context

Welcome to the workplace team. The meeting-room booking API needs a calendar behind it. The API in booking/day_calendar.py is agreed and stubbed out, booking/times.py is waiting for a time type, and the rules are in README.md.

Build both levels in 35 minutes. The checks are graded one by one, so each part you get working counts even if the rest is not done.

CAL-1: Book a slot or say it is taken (level 1)

Acceptance criteria

• check_availability(start, end) books a free slot and returns its id, counting up from 1; it returns -1 for a clash or a bad range.
• Bookings that only touch do not clash.
• bookings() lists every booking as [id, start, end], earliest first.

CAL-2: Times of day, cancelling and free slots (level 2)

Acceptance criteria

• book_time("HH:MM", "HH:MM") books with times of day, with "24:00" as the end of the day, and returns -1 for text that is not a time.
• cancel(booking_id) frees the slot; ids are never reused.
• free_slots(min_length) lists the free stretches of the day at least that long, earliest first.

Notes

• Run pytest tests/visible. The hidden checks cover clashes, edge times and free slots in more detail.
• Practice task modelled on a candidate report of a Microsoft calendar booking interview question. Original StackYard code, not the actual question; not affiliated with Microsoft.