fix: move from devenv to nix flake

.envrc

.gitlab-ci.yml

Taskfile.yml

devenv.nix

devenv.yaml

flake.lock

flake.nix

go.mod

nix/config/common-packages.nix

nix/config/defaults.nix

nix/config/release.nix

nix/config/release.nix.template

nix/packages/manual.nix

nix/scripts/bash-fkt.nix

nix/scripts/build-cover-report.nix

nix/scripts/build-manual.nix

nix/scripts/clean-up.nix

nix/scripts/go-task.nix

nix/scripts/release.nix

nix/scripts/run-ci-tests.nix