Validator not run with when constructing with `initialize`

[AntoinePrv]

Issue

This is a simple and successful validator test added in #252

number_bounded<double> n;
n.max = 10.;
REQUIRE_EQ(n.max(), 10.);
n.value = n.max() + 1.;
REQUIRE_EQ(n.max(), n.value());
n.value = n.min() - 1.;
REQUIRE_EQ(n.min(), n.value());
REQUIRE_THROWS_AS(n.min = n.max() + 1., std::runtime_error);
REQUIRE_THROWS_AS(n.max = n.min() - 1., std::runtime_error);

Replacing the first line with

auto n = number_bounded<double>::initialize().finalize();

And the test fails.