Fix pickling

Mostly reverts 739cb30d. Somehow, combining cached_property with the pickling of local classes leads to a weird error where, even though the customized DAQSettings object from daq.atsaverage.ATS9xx0.DAQSettings should be converted to a builtin dict in core._to_native_types(), there is still some reference to the DAQSettings object which cannot be pickled.

Since I don't feel like debugging this, just revert back to using regular propertys.

mentioned in commit 42bbe1d4

merged