I realized recently that my segwit implementation was not correct,
basically some time ago, wrongly reading the specs (and misleaded by
what follows), I thought that scriptsig would go into witness data as it
was, but that's not the case, op_pushdata is replaced by varlen

Now reading correctly the specs, they seem to be not totally correct,
then the first question is: why OP_0 is 00 in witness data and not 0100?
Does this apply to other op_codes? This does not look logical at all

The second question is: why for non segwit inputs there is a 00 length
in segwit data, what is the rational for that? It should just be nothing
since you don't need this to reconciliate things