message: Use byte buffers instead of char buffers
diff: @@ -56,10 +56,10 @@ struct fixture : test_coordinator_fixture<>, host_fixture {
  class dummy_application {
  public:
  - static expected<std::vector<char>> serialize(actor_system& sys,
  + static expected<std::vector<byte>> serialize(actor_system& sys,
  const type_erased_tuple& x) {
  - std::vector<char> result;
  - binary_serializer sink{sys, result};
  + std::vector<byte> result;
  + serializer_impl<std::vector<byte>> sink{sys, result};
  if (auto err = message::save(sink, x))
  return err;
  return result;
  @@ -77,7 +77,7 @@ public:
  }
  template <class Parent>
  - void handle_data(Parent&, span<char>) {
  + void handle_data(Parent&, span<byte>) {
  // nop
  }
  @@ -99,7 +99,7 @@ public:
  class dummy_application_factory {
  public:
  - static expected<std::vector<char>> serialize(actor_system& sys,
  + static expected<std::vector<byte>> serialize(actor_system& sys,
  const type_erased_tuple& x) {
  return dummy_application::serialize(sys, x);
  }
  