feat: Correct mypy type checking through PEP 561 (aws#5027)

Co-authored-by: parknate@ <[email protected]>
Co-authored-by: Molly He <[email protected]>

Author: 3 people

setup.py

@@ -58,7 +58,7 @@ def get_optional_dependencies():
     version=HERE.joinpath("VERSION").read_text().strip(),
     packages=find_packages("src"),
     package_dir={"": "src"},
-    package_data={"": ["*.whl"]},
+    package_data={"": ["*.whl", "py.typed"]},
     py_modules=[os.path.splitext(os.path.basename(path))[0] for path in glob("src/*.py")],
     include_package_data=True,
     install_requires=get_dependencies(),