Check and probably fix is_group_element type trait.

[martun]

For some reason nil::crypto3::algebra::is_field_element<nil::crypto3::algebra::fields::detail::element_fp<nil::crypto3::algebra::fields::paramsnil::crypto3::algebra::fields::pallas_base_field>>::value = true, but is_group_element<...> = false.

Yet every field element is also a group element.
Maybe something is wrong with this type trait:

crypto3-algebra/include/nil/crypto3/algebra/type_traits.hpp

Line 116 in ed5d8b4

struct is_group_element {