flake.nix,nix: use filesets to reduce unnecessary recompiles of packages #303

gitignore is removed because flakes only include things that are in git if using it (which tangled does). this one might be a bit confusing maybe but it does reduce recompilation by a lot since previously the packages just included the entire source.

this is not really maintainable; having to debug nix builds for every addition is a bit too limiting.

thats fair enough, was just experimenting. i might still experiment for this (was thinking of writing a small piece of nix code to make this automatic, so will probably do that and open a pr with that instead)