gh-101100: Fix sphinx warnings in Doc/library/functools.rst

[LamentXU123]

before:

C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:202: WARNING: py:func reference target not found: cache_info [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:207: WARNING: py:func reference target not found: cache_clear [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:287: WARNING: py:meth reference target not found: __lt__ [ref.meth]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:287: WARNING: py:meth reference target not found: __le__ [ref.meth]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:287: WARNING: py:meth reference target not found: __gt__ [ref.meth]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:287: WARNING: py:meth reference target not found: __ge__ [ref.meth]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:287: WARNING: py:meth reference target not found: __eq__ [ref.meth]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:420: WARNING: py:func reference target not found: abstractmethod [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:502: WARNING: py:func reference target not found: register [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:567: WARNING: py:func reference target not found: register [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:575: WARNING: py:func reference target not found: register [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:653: WARNING: py:func reference target not found: register [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:656: WARNING: py:func reference target not found: register [ref.func]
C:\Users\admin\Downloads\cpython-main\Doc\library\functools.rst:785: WARNING: py:func reference target not found: example [ref.func]

This PR fix them all, I will explain all my changes:

• link to cache_info and cache_clear are subpressed. Same to the formar subpressed link cache_parameters Create an index entries and anchor of cache_info and cache_clear
• __lt__ , __le__, __gt__, __ge__, __eq__ are magic methods of object. So It's changed to ~object.__lt__, etc.
• abstractmethod is actually referring to abc.abstractmethod. So it's changed to ~abc.abstractmethod
• register is actually a function of generic function. Since we don't get a doc about it., the link is supressed. Create an index entries and anchor of register
• example is an example function. The link is supressed.

Thanks!

The doc preview of this PR on this library: https://cpython-previews--136424.org.readthedocs.build/en/136424/library/functools.html

• Issue: Fix all Sphinx reference warnings in the documentation #101100

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📚 Documentation preview 📚: https://cpython-previews--136424.org.readthedocs.build/

[serhiy-storchaka]

It would be nice to add index entries and anchors for cache_info, cache_clear and register. You can use :no-typesetting: for this. For example:

.. method:: cache_info()
   :no-typesetting:

Check if this generates a nice index entry.