Add py.typed so consumers of vLLM can get type checking (#1509)

* Add py.typed so consumers of vLLM can get type checking

* Update py.typed

---------
Co-authored-by: aarnphm <29749331+aarnphm@users.noreply.github.com>
Co-authored-by: Zhuohan Li <zhuohan123@gmail.com>

setup.py

@@ -278,4 +278,5 @@ setuptools.setup(
     install_requires=get_requirements(),
     ext_modules=ext_modules,
     cmdclass={"build_ext": BuildExtension},
+    package_data={"vllm": ["py.typed"]},
 )

vllm/py.typed

+# Marker file for PEP 561.
+# The vllm package uses inline types.