fix: add py.typed marker for PEP 561 type hint support

[coolbeevip]

Description

Add py.typed marker for PEP 561 type hint support

This empty file marker tells type checkers that the package provides reliable type annotations, enabling better static analysis and IDE support. Follows PEP 561 specification for distributing and packaging type information.

https://peps.python.org/pep-0561/

Fixes: #1782

Checklist

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• [x] I have read the CONTRIBUTION guide (required)
• [x] I have linked this PR to an issue using the Development section on the right sidebar or by adding Fixes #issue-number in the PR description (required)
• [ ] I have checked if any dependencies need to be added or updated in pyproject.toml and uv lock
• [ ] I have updated the tests accordingly (required for a bug fix or a new feature)
• [ ] I have updated the documentation if needed:
• [ ] I have added examples if this is a new feature

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