gh-37807: Added some documentation in the developer's guide regarding deprecation
In PR #37721, I attempted to deprecate the ``ring`` keyword argument in
the ``matrix`` constructor
using ``@rename_keyword`` documented [here](https://doc.sagemath.org/htm
l/en/developer/coding_in_python.html#deprecation).
It did not work. The code compiled exactly as if the decorator wasn't
there.
I asked @mkoeppe why, he answered it "would be worth investigating and
documenting".
After some investigation, I came to the conclusion that developers
cannot use ``@rename_keyword`` and
other such decorators in Cython files.
My solution was to use ``deprecation_cython`` (this was accepted and
merged).
Since many other developers might end up having the exact same problem,
I simply suggest redirecting them
to ``deprecation_cython``, by adding what's necessary in the docs.
In this regard, I added a paragraph mentioning this in the Developer's
guide, as all of this was **totally absent** from documentation.
This way other developers won't need to investigate and spend time
debugging non-working code. :)
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URL: https://github.com/sagemath/sage/pull/37807
Reported by: SandwichGouda
Reviewer(s): Matthias Köppe
