Explore simplification of the internals of builders 2D and more

[tpadioleau]

Similar to #945, as the batched dimensions are no longer part the class templates, the builders m_spline_builder_type1 and builder_deriv_type1 stored in the 2d builder hve the same type., see

ddc/include/ddc/kernels/splines/spline_builder_2d.hpp

Lines 198 to 199 in ca17d55

	builder_type1 m_spline_builder1;
	builder_deriv_type1 m_spline_builder_deriv1;

They are constructed with different input parameters. We should explore whether it impacts the performance to only use a single builder.