replace environment variable with nixpkgs directory

In this directory we generate all the files that we need to load nixpkgs.
This seems more robust than all those environment variables that may or not may be set.

pkgs/clan-cli/shell.nix

@@ -18,29 +18,20 @@ pkgs.mkShell {
     self.packages.${pkgs.system}.nix-unit
     pythonWithDeps
   ];
-  CLAN_FLAKE = self;
-  # This is required for the python tests, where some nix libs depend on nixpkgs
-  CLAN_NIXPKGS = pkgs.path;
   # sets up an editable install and add enty points to $PATH
   # This provides dummy options for testing clan config and prevents it from
   # evaluating the flake .#
   CLAN_OPTIONS_FILE = ./clan_cli/config/jsonschema/options.json;
+  PYTHONPATH = "${pythonWithDeps}/${pythonWithDeps.sitePackages}";
   shellHook = ''
     tmp_path=$(realpath ./.direnv)
-    repo_root=$(realpath .)
-    mkdir -p "$tmp_path/python/${pythonWithDeps.sitePackages}"
-
-    ${pythonWithDeps.interpreter} -m pip install \
-      --quiet \
-      --disable-pip-version-check \
-      --no-index \
-      --no-build-isolation \
-      --prefix "$tmp_path/python" \
-      --editable $repo_root
-
+                                      
+    rm -f clan_cli/nixpkgs
+    ln -sf ${clan-cli.nixpkgs} clan_cli/nixpkgs
+    
     export PATH="$tmp_path/bin:${checkScript}/bin:$PATH"
-    export PYTHONPATH="$repo_root:$tmp_path/python/${pythonWithDeps.sitePackages}:${pythonWithDeps}/${pythonWithDeps.sitePackages}"
-
+    export PYTHONPATH="$PYTHONPATH:$(pwd)"
+    
     export XDG_DATA_DIRS="$tmp_path/share''${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}"
     export fish_complete_path="$tmp_path/share/fish/vendor_completions.d''${fish_complete_path:+:$fish_complete_path}"
     mkdir -p \