"hlt2" or "spruce" assert decorator or assert made part of the "base class" shared for HLT2 and Sprucing lines

see discussion reported in:

!850 (comment 4501283)

concerning:

• https://gitlab.cern.ch/lhcb/Moore/-/blob/b2oc_upgrade/Hlt/Hlt2Conf/python/Hlt2Conf/lines/b_to_open_charm/b_to_dh.py
• https://gitlab.cern.ch/lhcb/Moore/-/blob/b2oc_upgrade/Hlt/Hlt2Conf/python/Hlt2Conf/lines/b_to_open_charm/b_to_dhh.py