Consider using flags to customize `ArrayOutputMixin`

[arcondello]

E.g., imagine that you want to disallow an ArrayNode from ever being dynamic. It might be nice to be able to specify that as a template argument to ArrayOutputMixin. This would allow is to combine different flags like the one we already added to ScalarOutputMixin in #271.

Something like

enum class ArrayMixinFlags {
    // default is sometimes dynamic
    AlwaysDynamic = 1 << 0,
    NeverDynamic = 1 << 1,

    // default is not to provide a state implementation
    ProvideState = 1 << 2,
};

template <class Base, ArrayMixinFlags Flags = 0>
class ArrayOutputMixin : public Base {
    template <std::ranges::sized_range Range>
    explicit ArrayOutputMixin(Range&& shape)
            : ndim_(shape.size()), shape_(make_shape(std::forward<Range>(shape))) {
        if constexpr (Flags && ArrayMixinFlags::NeverDynamic) {
            // throw an error if dynamic
        }
    }

    ...
};


class NeverDynamicNode : public ArrayOutputMixin<ArrayNode, ArrayMixinFlags::NeverDynamic> {
    ...
};

class NeverDynamicAndDefaultStateNode : public ArrayOutputMixin<ArrayNode, ArrayMixinFlags::NeverDynamic | ArrayMixinFlags::ProvideState> {
    ...
};