[python-package] declare the use of inline type hints (#5709)

python-package/MANIFEST.in

@@ -1,7 +1,7 @@
 prune build
 include LICENSE
 include *.rst *.txt
-recursive-include lightgbm VERSION.txt *.py *.so
+recursive-include lightgbm VERSION.txt py.typed *.py *.so
 include compile/CMakeLists.txt
 include compile/cmake/IntegratedOpenCL.cmake
 recursive-include compile *.so

python-package/setup.py

@@ -389,4 +389,5 @@ if __name__ == "__main__":
                        'Programming Language :: Python :: 3.8',
                        'Programming Language :: Python :: 3.9',
                        'Programming Language :: Python :: 3.10',
-                       'Topic :: Scientific/Engineering :: Artificial Intelligence'])
+                       'Topic :: Scientific/Engineering :: Artificial Intelligence',
+                       'Typing :: Typed'])