dev: use low level ret after an assert 0 = 1

[ClementWalter]

Why

In some places, we need to raise surely with an assert 0 = 1 (branch should not be run) nut still need to return something to comply with the compiler expected return type.

Currently, we build useless objects that are actually never returned, and it impacts falsy the coverage.

What

Don't build fake object for the sake of making the compiler happy.

How

Just use a low level ret.