* fix: add missing std::forward calls

Two of the four cpp_function overloads are missing std::forward calls, which seems like a simple oversight.

* add test for https://github.com/pybind/pybind11/pull/3443

* add py tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix test

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>