feat(flake): remove impurity, update nix-direnv

Use path as an input that can be overriden automatically when direnv is
in use.
nix-direnv version present in .envrc has been updated, using watch_file on the flake is already handled.

.envrc

@@ -1,10 +1,9 @@
-if ! has nix_direnv_version || ! nix_direnv_version 2.2.1; then
-    source_url 'https://raw.githubusercontent.com/nix-community/nix-direnv/2.2.1/direnvrc' 'sha256-zelF0vLbEl5uaqrfIzbgNzJWGmLzCmYAkInj/LNxvKs='
+if ! has nix_direnv_version || ! nix_direnv_version 3.0.5; then
+  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.5/direnvrc" "sha256-RuwIS+QKFj/T9M2TFXScjBsLR6V3A17YVoEW/Q6AZ1w="
 fi
 
-watch_file flake.nix
-watch_file flake.lock
-
-if ! use flake . --impure; then
+DEVENV_ROOT_FILE="$(mktemp)"
+printf %s "${PWD}" > "${DEVENV_ROOT_FILE}"
+if ! use flake . --override-input devenv-root "file+file://${DEVENV_ROOT_FILE}"; then
     printf '%s\n' "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

flake.nix

@@ -4,6 +4,11 @@
   inputs = {
     devenv.url = "github:cachix/devenv";
 
+    devenv-root = {
+      url = "file+file:///dev/null";
+      flake = false;
+    };
+
     flake-parts = {
       url = "github:hercules-ci/flake-parts";
       inputs.nixpkgs-lib.follows = "nixpkgs";
@@ -53,9 +58,14 @@
                 #
                 # Thank you! -Xarvex
 
-                name = "TagStudio";
+                devenv.root =
+                  let
+                    devenvRoot = builtins.readFile inputs.devenv-root.outPath;
+                  in
+                  # If not overriden (/dev/null), --impure is necessary.
+                  pkgs.lib.mkIf (devenvRoot != "") devenvRoot;
 
-                dotenv.disableHint = true;
+                name = "TagStudio";
 
                 # Derived from previous flake iteration.
                 packages = (with pkgs; [