Make1_generic is for blitting between two values of the same container type that's
not fully polymorphic (in the sense of Container.Generic).
val blit : ('a t, 'a t) Base__.Blit_intf.blitval blito : ('a t, 'a t) Base__.Blit_intf.blitoval unsafe_blit : ('a t, 'a t) Base__.Blit_intf.blitval sub : ('a t, 'a t) Base__.Blit_intf.subval subo : ('a t, 'a t) Base__.Blit_intf.subo