FR: Add "Supported Signatures" Section to the NumPy Docstring Style Guide

Python doesn't natively support function overloading (like how C++ does), but imitates it with optional positional and keyword arguments. With the advent of the typing.overload decorator, we have the ability to express correlations between parameter and return types. C/C++ and Fortran methods ported to Python sometimes have function overloads that differ in arity and type. For polymorphic functions, it would be nice to have a section in the docstring describing the accepted signatures for a function.

A suggestion (dummy example) of what this might look like is:

from __future__ import annotations

from collections.abc import Sequence


def double(input_: int | Sequence[int]) -> int | list[int]:
    """Returns the input doubled.

    If the input is a sequence, returns the sequence
    with every item doubled. Otherwise, it returns
    the passed number doubled.

    Parameters
    ----------
    input_ : int or Sequence[int]
        The number (or number array) to be doubled

    Supported Signatures
    --------------------
    double( int ) -> int
    double( Sequence[int] ) -> list[int]

    Returns
    -------
    int or list[int]
        The input doubled if the input is a single ``int``,
        else the list with its elements doubled.
    """
    ...

Start by locating the NumPy docstring style guide and the existing section-handling documentation or tests in this repository. Compare the proposed “Supported Signatures” example with current conventions, then define completion as documented, consistently formatted support for the new section and coverage for the demonstrated signatures.