maketx perf: make copy_block use iterators and specialized types
maketx perf: make copy_block use iterators and specialized types

OpenImageIO/oiio,lgritz/oiio,scott-wilson/oiio,OpenImageIO/oiio,OpenImageIO/oiio,bdeluca/oiio,micler/oiio,micler/oiio,bdeluca/oiio,lgritz/oiio,cwilling/oiio,scott-wilson/oiio,OpenImageIO/oiio,cwilling/oiio,mcanthony/oiio,mcanthony/oiio,sambler/oiio,lgritz/oiio,scott-wilson/oiio,micler/oiio,cwilling/oiio,sambler/oiio,YangYangTL/oiio,YangYangTL/oiio,cwilling/oiio,bdeluca/oiio,lgritz/oiio,micler/oiio,YangYangTL/oiio,mcanthony/oiio,bdeluca/oiio,scott-wilson/oiio,sambler/oiio,mcanthony/oiio,YangYangTL/oiio,sambler/oiio