Remove unnecessary dimensionality checks

        auto fallback_field = config_.get<ROOT::Math::XYZVector>("magnetic_field_fallback", ROOT::Math::XYZVector());

        auto field_data = read_field();

        auto dims = field_data.getDimensionality(); // Vector dimensionality of the field (should be 3 for B-field)

        if(dims != 3) {

            throw std::invalid_argument("B-field vectors were not three dimensional.");

        }

        auto dims = field_data.getDimensionality(); // Vector dimensionality of the field (will be 3 for B-field)

        auto cellsize = field_data.getSize();       // Physical dimensions for each cell in the field mesh

        auto ncells = field_data.getDimensions();   // Number of cells in each direction of the field mesh

        auto field_mesh = field_data.getData();     // The field mesh B-field data as a flattened array

        if(ncells[0] * ncells[1] * ncells[2] * dims != field_mesh->size()) {

            throw std::invalid_argument("B-field does not span the given dimensions");

        }

        MagneticFieldFunction function =

            [fallback_field, field_mesh, cellsize, ncells, dims](const ROOT::Math::XYZPoint& coord) {

                // Find the nearest field mesh cell to the given input coordinate (assuming the mesh is centred about the