fix: debug error when std::option value_or is used.

The recently introduced vector definition using std::optional::value_or

    std::vector<double> values = value_data.value_or(*values_data);

leads to the following fatal error during debugging:

/usr/include/c++/15.2.1/optional:1179: constexpr const _Tp& std::optional<_Tp>::operator*() const & [with _Tp = std::vector<double>]: Assertion 'this->_M_is_engaged()' failed.

The reason is: if values_data is disengaged, *values_data triggers the std::optional debug-mode assertion.

This MR fixes the error by replacing the vector definition with the following safe ternary operator:

    std::vector<double> values =
        value_data ? *value_data
                   : (values_data ? *values_data : std::vector<double>{});

• TODO: provide short description of the changes.

1. Feature description was added to the changelog
2. Tests covering your feature were added?
3. Any new feature or behaviour change was documented?