Fine-tuning of optical properties with salts of discrete or polymeric, heterobimetallic telluride anions [M$_4$($\mu_4$-Te)(SnTe$_4$)$_4$]$^{10-}$ (M = Mn, Zn, Cd, Hg) and $^3_∞${[Hg$_4$($\mu_4$-Te)(SnTe$_4$)$_3$]$^{6-}$}