Add heating schedule setter for circuits

[lackas]

Summary

Adds methods to set heating circuit schedules:

• setHeatingSchedule(schedule) - set the heating schedule for a circuit
• getHeatingScheduleModes() - get available schedule modes (e.g., reduced, normal, fixed)

This complements the existing getHeatingSchedule() method and follows the same pattern as setDomesticHotWaterCirculationSchedule().

Fixes #539

Test plan

• Added test for getHeatingScheduleModes() using Vitocal300G test data
• All tests pass

[lackas]

See also PR #368 which adds setDomesticHotWaterSchedule() - similar pattern for DHW schedules.

[CFenner]

Can we type this?

[lackas]

Sure! The schedule structure is a nested dict (day keys → list of time slot dicts), so the most accurate type would be quite verbose. Would dict be sufficient, or do you have something more specific in mind? Note that the existing setDomesticHotWaterCirculationSchedule has the same untyped schedule parameter — happy to type that one too while we're at it.

[CFenner]

Then lets go with a dict, the we at least have something.

[lackas]

@CFenner Friendly ping — any thoughts on the typing approach for the schedule parameter? Happy to go with dict or something more specific, whatever you prefer.

[lackas]

Added dict type hint to setHeatingSchedule and list return type to getHeatingScheduleModes. Rebased on latest master. Ready for review.