By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Run the internet-dependent tests purely too, via the pure-impure trick Instead of a separate impure NixCI test job, wrap the handful of tests that need real network access in a fixed-output derivation (the pure-impure trick, duplicated from NorfairKing/pure-impure-nix). Nix grants FODs network access, so these now run inside `nix flake check` as well. The heavy offline suite stays a normal, fully reproducible pure build. Removes nix-ci.nix and packages.impure-test.
| Time to Start | Worker time | Duration | Time to finish | Idle | |
| Config | 0s | 7s | 7s | 7s | 0s |
| Eval | 7s | 19s | 19s | 27s | 0s |
| Build | 16s | 27s | 1m29s | 1m45s | 1m18s |
| Suite | 0s | 54s | 1m45s | 1m45s | 1m18s |