parse cash discounts

[jstaerk]

when parsing (extractInto) a xrechnung like this

response_1737188708542_xr_skonto.txt

or a zugferd extended like that

response_1737188825551_ext_skonto.txt

the returned invoice should include a cashdiscount object in the cashdiscounts list, to the effect that a serialized cashdiscounts looks similar to this

 "cashDiscounts": [
        {
            "days": 14,
            "percent": 2
        }
    ],