add Lambert W function support to expression compiler

[crowlogic]

then calculate the (co)variance structure of

$$\zeta \left(\frac{1}{2}+\frac{\mathrm{i} \left(8 n-3 \right) \pi}{4 W \left(\frac{8n-3}{8 {\mathrm e}}\right)}\right) {\mathrm e}^{\mathrm{i} \left(\arg \left(\Gamma \left(\frac{1}{4}+\frac{\mathrm{i} \left(8n-3\right) \pi}{8 W\left(\frac{8n-3}{8 {\mathrm e}}\right)}\right)\right)-\frac{\left(8n-3 \right) \pi \ln \left(\pi \right)}{8 W\left(\frac{8n-3}{8 {\mathrm e}}\right)}\right)}$$

[crowlogic]

dont think the answer will invole it so tabling it until theres an actual need