* Adds set_name method of pybind11::capsule class

This calls PyCapsule_SetName on the underlying capsule object.

modified destructors to query capsules's Name

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Handle possible exception thrown by PyCapsule_GetName

Also removed accidentally reintroduced use of `const char *&`.

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Fixed function name

* Introduced private static function to reuse get_name_or_throw

* added tests for capsule renaming

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* handle python error in flight

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* Initialized PyObject * variables to nullptr

* use write-unraisable if PyCapsule_GetName raises

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* get_name_or_throw->get_name_no_throw

If PyCapsule_GetName raises an error we should write as unraisable
to consume it and notify user, and then restore the error in flight if any.
This way this method called from destructor would not modify interpreter
error state.

* used error_scope struct

* Renamed get_name_no_throw->get_name_in_error_scope

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