Insert `Z.of_nat` when coercion is dropped.

theories/lang/heap.v

theories/lang/lang.v

theories/lang/lib/arc.v

theories/lang/lib/memcpy.v

theories/lang/lib/new_delete.v

theories/lang/lib/swap.v

theories/lang/lifting.v

theories/lang/proofmode.v

theories/typing/base.v

theories/typing/examples/nonlexical.v

theories/typing/lib/arc.v

theories/typing/lib/brandedvec.v

theories/typing/lib/cell.v

theories/typing/lib/ghostcell.v

theories/typing/lib/join.v

theories/typing/lib/mutex/mutex.v

theories/typing/lib/option.v

theories/typing/lib/rc/rc.v

theories/typing/lib/rc/weak.v

theories/typing/lib/refcell/refcell_code.v