add narwhals to deps

Author: schloerke

setup.cfg

@@ -58,6 +58,7 @@ install_requires =
     # https://github.com/posit-dev/py-shiny/issues/1114#issuecomment-1942757757
     python-multipart>=0.0.7;platform_system!="Emscripten"
     setuptools;python_version>="3.12"
+    narwhals>=1.1.7
 tests_require =
     pytest>=3
 zip_safe = False