* Allow specializations based on callback function return values.

* clang-tidy auto fix

* Add a test case for function specialization.

* Add test for callback function that raises Python exception.

* Fix test failures.

* style: pre-commit fixes

* Add `#define PYBIND11_HAS_TYPE_CASTER_STD_FUNCTION_SPECIALIZATIONS`

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Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>