Add Typing Stubs

Nowadays many tools(like `mypy` or `pyright`) start to provide type check. Would this project add typing stubs in the future?

The issue names no files, tests, or entry points; it only references mypy and pyright as possible consumers. Start by surveying the project’s Python package and deciding the scope of stub coverage, then define validation with those type checkers. Done means the agreed public API has usable typing stubs and type-checking behavior is verified.

Written by the indexing model from the issue text.