Restore the TMP, TEMP, TMPDIR, TEMPDIR variables to their previous
values if `use flake` modified them in `.envrc`.
Signed-off-by: Philipp Jungkamp <Philipp.Jungkamp@opal-rt.com>
Add an `.envrc` file and add the `.direnv` directory to `.gitignore`.
`direnv` will check whether `nix` is available and `flakes` are enabled
before trying to load the environment from `packaging/nix`.
Using flakes from the `direnv` stdlib requires `direnv 2.30.0` or later.
Signed-off-by: Philipp Jungkamp <philipp.jungkamp@rwth-aachen.de>
