Static case for rational order

[mforets]

In #135 we admit integer orders for linear reachability algorithms that use statically sized arrays; if the initial set has not max_order, we append zeros in _reconvert(Ω0::Zonotope{N, VN, MN}, static::Val{true}, dim::Val{n}, ngens::Val{p}). That code assumes that the order is an integer. If it is a rational we may have to change some internals.