merkle_tree: speed up size_detail_node/3
merkle_tree: speed up size_detail_node/3

-> instead of appending lists, allow a list of lists
tectronics/scalaris,seyyed/scalaris,digshock/scalaris,seyyed/scalaris,tectronics/scalaris,seyyed/scalaris,digshock/scalaris,seyyed/scalaris,tectronics/scalaris,digshock/scalaris,seyyed/scalaris,tectronics/scalaris,digshock/scalaris,seyyed/scalaris,digshock/scalaris,tectronics/scalaris,digshock/scalaris,seyyed/scalaris,digshock/scalaris,tectronics/scalaris,tectronics/scalaris