split_solutionGiven a named list mapping variable ids to their (shape-aligned)
deltas, packs them into a single length-x_length numeric vector
in var_id_to_col order. Mirrors ParamConeProg.split_adjoint
in cone_matrix_stuffing.py:304-318.
split_adjoint(param_prog, del_vars)Numeric vector of length x_length.
A ParamConeProg.
A named list of as.character(var_id) -> array.