refactor docstrings in `draw`, `classification`, and `key_points` (#2161)

* refactor docstrings in draw, classification, and key_points
* Refactor type annotations, logging, and empty output handling across key modules
* Refactor type annotations in `core.py` to include conditional `TYPE_CHECKING` for `torch` imports
* Apply suggestions from code review

---------

Co-authored-by: Jirka Borovec <6035284+Borda@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>