Add custom parser for cleaned data

[dunderrrrrr]

It would be nice to add an argument to at that returns a cleaned json. Currently, at() just returns the raw results. You should atleaset have an option to have everything returned in a cleaned way.

Example:

>>> from skolmaten import SchoolFood
>>> food = SchoolFood(school="0b4d4d77-7b27-4591-a03e-28309e039b1e")
>>> food.at(2025, 10) # returns a huge json with some irrelevant data

>>> food.at(2025, 10, cleaned=True)
{
    "2025-01-01": ["Hamburgare", "Köttbullar och potatismos"]
    "2025-01-02": ["Korvstroganoff och ris", "Plankstek"]
    ...
}

or just some object

>>> food.at(2025, 10, cleaned=True)
{
    Food(...),
    Food(...),
    Food(...),

}