NumCosmoMathPowspecCorr3dset_best_lnr0

Sets the value of $\ln(r_0)$ which gives the best results for the transformation based on the current value of $\ln(k_0)$, this is based in the rule of thumb $\mathrm{max}_{x^}(j_l)$ where $ x^ \approx l + 1$ (see ncm_fftlog_sbessel_j_set_best_lnr0()).