The nix-shell advice is cogent enough that somebody might use it. Instead of a bare bash script, consider direnv, which scopes each shell session to a directory and has upstream builtin Nix support.
Edit: When laning with two mages in bot, focus on harassing enemy champions instead of farming. For Veigar, line up each Q to hit a minion and a champion, combining the farm and harass into a single action. Do not be aggressive in the early game; AP takes time to build. The deaths at 13min and 15min were due to aggression, and by 18min it looks like tilt. Ward more; at 22min, Veigar is alone in lane with no visibility into nearby bushes, and 4/5 enemy champions can burst him down if he misses his cage. Rod of Ages is a good call, but an Hourglass would be an even better call, as it can nullify damage from Ahri and Zed combos. Finally, don't do fadeaway ults at the end of Veigar combos; it feels satisfying, but isn't as much damage as carefully-timed Q.