clan-cli: Add ruff to devShell again. Add missing type annotations

pkgs/clan-cli/shell.nix

@@ -14,11 +14,11 @@ mkShell {
       ps:
       with ps;
       [
-        ruff
         mypy
       ]
       ++ (clan-cli.devshellPyDeps ps)
     ))
+    ruff
     nix-unit
   ] ++ clan-cli.runtimeDependencies;
 
@@ -33,6 +33,8 @@ mkShell {
     export PKG_ROOT="$GIT_ROOT/pkgs/clan-cli"
     export PYTHONWARNINGS=error
 
+    export CLAN_CORE_PATH="$GIT_ROOT"
+
     # Add current package to PYTHONPATH
     export PYTHONPATH="$PKG_ROOT''${PYTHONPATH:+:$PYTHONPATH:}"