feat req: mypy type stubs

[crdrost]

I would like to be able to typecheck usage of aws_encryption_sdk using the new MPL lib.

I was able to generate some local stubs with

$ poetry run stubgen -o types -p 'aws_encryption_sdk'                                                                    2 ↵
Processed 42 modules
Generated files under types/aws_encryption_sdk/

but stubgen on the smithygenerated stuff causes some pickling error,

$ poetry run stubgen -p aws_cryptographic_material_providers
Traceback (most recent call last):
  File "/opt/homebrew/Cellar/[email protected]/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/queues.py", line 244, in _feed
    obj = _ForkingPickler.dumps(obj)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/reduction.py", line 51, in dumps
    cls(buf, protocol).dump(obj)
TypeError: cannot pickle 'module' object

[ ... some time later ... ]

Traceback (most recent call last):
  File "/Users/cdrost/Library/Caches/pypoetry/virtualenvs/project-sGieSmVg-py3.11/bin/stubgen", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "mypy/stubgen.py", line 1989, in main
  File "mypy/stubgen.py", line 1776, in generate_stubs
  File "mypy/stubgen.py", line 1530, in collect_build_targets
  File "mypy/stubgen.py", line 1557, in find_module_paths_using_imports
  File "mypy/stubutil.py", line 81, in walk_packages
  File "mypy/moduleinspect.py", line 146, in get_package_properties
  File "mypy/moduleinspect.py", line 172, in _get_from_queue
RuntimeError: Timeout waiting for subprocess

Since apparently it's all autogenerated from dafny anyways it seems like it might be tractable for AWS to just publish proper type stubs for aws_cryptographic_material_providers?