feat(hot-water): ASHW cylinder support validated on an EDL200UK-630RF

[Mista-P]

Summary

Support for air-source heat pump hot water cylinders (ASHW Cylinder), from a live EDL200UK-630RF compared against the official app at the same moment.

Stacked on #127 (integer ErrorCode/WarningCode), which the cylinder needs: it is the appliance that sends them as integers. Please merge #127 first; this PR's own changes are the last three commits.

fix(capabilities): a cylinder is not room climate. The cylinder reports its water target (45 °C) in ActiveSetPointTemperature, so capabilities_for called it room climate and kept every room-heater feature. A client then shows a thermostat with a 7–30 °C range plus room temperature, open window, EcoStart and setback. Now only a RoomTemperature makes a hot-water appliance room climate. Without one, the room-heater features default to off unless the status reports them (this cylinder sends null for all of them), and so do setpoint_write/setback_write. Room heaters are unchanged, and test_status_marks_features_and_hot_water still holds.

feat(hot-water):

• ApplianceStatus declares the cylinder fields the overview already carries: Capacity, HeatingUp, IsGreenEnergyActive, HygieneFrequency, HygieneTemperature, HolidayNumOfDays, plus the always-null rest. AvailableHotWater turns out to be litres, since the app shows "336 L Hot water" for 336.
• get_heat_pump_hot_water_schedule now returns a new HeatPumpHwcSchedule. The real reply is {HubId, ApplianceId, TimerPeriods: [{DayOfWeek, StartTime: 0, Mode: 2}]}: no TimerMode, integer start times, a mode per period. Parsing it as TimerModeSettings raised on real hardware.
• New set_hot_water_holiday(hub_id, appliance_ids, until, *, enable, heat_pump). Verified live: SetApplianceModeHeatPumpHwc with ApplianceModes=8, Status=1 moved the status 8192 → 8200 with HolidayNumOfDays set and heating stopped, and Status=0 restored 8192. The cylinder counts whole days, so until is also sent as a rounded-up NumberOfDays.
• set_heat_pump_hot_water_schedule is unchanged but now documents that UpdateHeatPumpHwcSchedulePeriods answered 403 to every body tried: wrapped in TimerModeSettings or Settings, with or without TimerMode, integer or HH:MM:SS times, app_version up to 3.0.0. Unwrapped bodies got 400. The app's own request hasn't been captured.

docs: the decompiled API reference, OpenAPI summaries and README now say what was validated on the cylinder and what still wasn't (temperature, boost and hygiene writes).

Still unknown: what the schedule's Mode values mean (only 2 seen), whether StartTime is minutes after midnight, and how the app derives the fill percentage it shows.

Testing

• New tests built from the live replies: capabilities for the cylinder (with and without a room temperature), ApplianceStatus with every cylinder field, the schedule read, and the holiday request bodies (on, off, non-heat-pump endpoint, missing end).
• ruff check, ruff format --check, mypy, pytest (207 passed) and pre-commit run --all-files pass.
• The Home Assistant integration PR runs on the same cylinder with these findings.

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