* Added `PyRef::as_super` and `PyRefMut::as_super` methods, including docstrings and tests. The implementation of these methods also required adding `#[repr(transparent)]` to the `PyRef` and `PyRefMut` structs.
* Added newsfragment entry.
* Changed the `AsRef<U>`/`AsMut<U>` impls for `PyRef` and `PyRefMut` to use the new `as_super` methods. Added the `PyRefMut::downgrade` associated function for converting `&PyRefMut` to `&PyRef`. Updated tests and docstrings to better demonstrate the new functionality.
* Fixed newsfragment filename.
* Removed unnecessary re-borrows flagged by clippy.
* retrigger checks
* Updated `PyRef::as_super`, `PyRefMut::as_super`, and `PyRefMut::downgrade` to use `.cast()` instead of `as _` pointer casts. Fixed typo.
* Updated `PyRef::as_super` and `PyRefMut::downgrade` to use `ptr_from_ref` for the initial cast to `*const _` instead of `as _` casts.
* Added `pyo3::internal_tricks::ptr_from_mut` function alongside the `ptr_from_ref` added in PR #4240. Updated `PyRefMut::as_super` to use this method instead of `as *mut _`.
* Updated the user guide to recommend `as_super` for accessing the base class instead of `as_ref`, and updated the subsequent example/doctest to demonstrate this functionality.
* Improved tests for the `as_super` methods.
* Updated newsfragment to include additional changes.
* Fixed formatting.
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Co-authored-by: jrudolph <jrudolph@anl.gov>
JRRudy1