Conversion from zonotopic set to Hyperrectangle

[mforets]

I see it can be useful syntax, but slightly confusing, given that only works for some but not (actually most) zonotopes? While in the other direction it always works. I'd rather not have this method, and in practice suggest using overapproximate(Hyperrectangle, Z::Zonotope).

EDIT: I see it can be useful syntax for exact conversions, so I'll approve it.

[schillic]

Unfortunately, I do not remember why I suggested this PR. I would now agree to use overapproximate(Z::Zonotope, Hyperrectangle). The implementation here is probably more efficient, but it is true that it only applies in rare cases. Nevertheless, Julia generally allows convert even if most inputs are invalid:

julia> convert(Int, 1.0)
1

julia> convert(Int, 1.1)
ERROR: InexactError: Int64(1.1)

In that light, I think we can add this method.