Add TEMPLATE_TEST_CASE to our tests to improve function coverage

Currently, most tests are a simple SCENARIO that tests the templated code only for real_t as template argument. We should cover the other relevant types too, e.g. using TEMPLATE_TEST_CASE.

Typically, this type list is: float, double, std::complex<float>, std::complex<double> (except in some cases where complex numbers do not make sense). For DataContainer there is also index_t.