Fix and guard against erroneous use of list context in internal DBIC code

Fix and guard against erroneous use of list context in internal DBIC code

This situation is dangerous in case the end-user employs something like
DBIx::Class::Helper::ResultSet::IgnoreWantarray

Besides the trivial fix in ::Row::copy, this commit introduces the
DBIC_ASSERT_NO_INTERNAL_WANTARRAY=1 mechanism (which will be
automatically picked up and engaged by our CI due to eed5492f). As a
bonus the check is usable on DBIC dependencies as well.