"Monkey-patch inspect.isfunction() to support Cython functions."

Introduced in 2018 (8.3.beta2) in #25373 (for #24994).

However, this change has been rejected by upstream (https://bugs.python.org/issue30071, https://www.python.org/dev/peps/pep-0575/, https://www.python.org/dev/peps/pep-0580/).

In this ticket:

• we remove the monkey-patching

• replace unnecessary uses of inspect in ordinary Sage library code by other solutions

• replace remaining uses of inspect.isfunction by the new name of our monkey-patched variant: sage.misc.sageinspect.is_function_or_cython_function

(To be checked whether https://www.python.org/dev/peps/pep-0590, superseding some of the above rejected PEPs, offers help; see also the informational PEP https://www.python.org/dev/peps/pep-0579/)

Related:

• Use Cython directive binding=True to get signatures for cython methods #26254 No signature shown in help for cythonized built-in methods
• Use sphinx.util.inspect.Signature not sphinx.ext.autodoc.inspector.formatargspec #27578 Use sphinx.util.inspect.Signature, not sphinx.ext.autodoc.inspector.formatargspec
• sage_getargspec mishandles keyword-only arguments #31309 sage_getargspec mishandles keyword-only arguments

Depends on #31420

CC: @fchapoton @kwankyu @jhpalmieri @orlitzky

Component: refactoring

Author: Matthias Koeppe

Branch/Commit: 2ba4c43

Reviewer: Michael Orlitzky

Issue created by migration from https://trac.sagemath.org/ticket/32479