Use SET_IMPL_MACRO for metaop.

Fix issue encountered by @wboussella

By not using the MACRO we encountered the issue: https://github.com/pybind/pybind11/issues/4417

added Fix 🔥🔥 label

assigned to @cmoineau

enabled an automatic merge when all merge checks for b29f4d7b pass

changed milestone to %aidge v0.6.0

@pineapple This is a quick fix to unlock @wboussella

merged

mentioned in commit a7ec11eb