NumCosmoWLEllipticitySeriesTraceDeteval

Refills ser‘s chi and jac series (see nc_wl_ellipticity_series_trace_det_get_chi()/ _get_jac()) at $\chi_L=\rho\,w$.

eps: $\chi_I(\chi_L,g)=(\chi_L-g)/(1-g\chi_L)$, closed form, no recursion: $c_0=\chi_L={1{:}\rho}$; $c_k=\chi_L^{k-1}(\chi_L^2-1)= \rho^{k+1}w^{k+1}-\rho^{k-1}w^{k-1}$ for $k\ge1$ — a 2-term Laurent series at every order, written directly into ser‘s own stable slots (no scratch needed at all).

eps: $f_\mathrm{eps}’(\chi_L,-g)=(1-g^2)/(1-g\chi_L)^2$ Taylor-in-$g$ coefficients — closed form: $1/(1-g\chi_L)^2=\sum_n(n+1)\chi_L^n g^n$ (literal binomial series, single-term at harmonic $n$ each), times $(1-g^2)$. $\mathrm{Jac}=|\mathrm{that}|^2$ is this series convolved with its own conjugate. Also fills nc_wl_ellipticity_series_trace_det_get_abs_sq() ($|\chi_I(\chi_L,g)|^2=\chi_I\overline{\chi_I}$, population-independent, exactly the $\rho^2(g)$ input nc_galaxy_shape_pop_eval_p_rho2_g_series() needs), since it’s a pure function of chi already computed here.