Properly copy attributes of CONTROL key leafs and RUN-only keys

The attribute copy implementation so far only looked at the attributes of CONTROL key parents, ignoring those on the .value. and .timestamp leafs. In addition, the attributes of RUN-only keys were lost entirely. This MR fixes this by maintaining all attributes.

@kluyvert While the attributes on leafs seem to be a subset of the parent attributes in almost all cases and/or carry incorrect values for duplicates (daqPolicy has the correct value on the parent, but always 1 on the leaf), I spotted a few keys only existing on leafs. Since EXtra-data only exposes the leaf attributes right now, this seems prudent. It's another unfortunate consequence of this mix of parent, .value and .timestamp...