Multiple is_prime implementations

[VincentRouvreau]

I can see multiple _is_prime implementations in Persistence_matrix module:

• gudhi-devel/src/Persistence_matrix/include/gudhi/Fields/Zp_field.h

  Line 405 in f23c154

  static constexpr bool _is_prime() {

• gudhi-devel/src/Persistence_matrix/include/gudhi/Fields/Multi_field_small_operators.h

  Line 493 in f23c154

  inline constexpr bool Multi_field_operators_with_small_characteristics::_is_prime(const int p) {

• gudhi-devel/src/Persistence_matrix/include/gudhi/Fields/Multi_field_small.h

  Line 390 in f23c154

  static constexpr bool _is_prime(const unsigned int p) {

• gudhi-devel/src/Persistence_matrix/include/gudhi/Fields/Multi_field_operators.h

  Line 440 in f23c154

  static constexpr bool _is_prime(const int p) {

• a new implementation that comes with Ripser new module : https://github.com/mglisse/gudhi-devel/blob/8cab8c9e3695846278f3b8fd8095715bbc8e5950/src/Ripser/include/gudhi/ripser.h#L158

We could also take the opportunity to homogenize the behaviour of Ripser/Matrix/Persistent_cohomology when passing a homology coefficient field.