chr: Accept SupportsIndex argument (#13494)

The `chr` function does accept objects that implement the
`SupportsIndex` protocol. The [implementation] of the builtin method
calls `PyLong_AsLongAndOverflow` on the argument, which in turn calls
`__index__()`, if present. The parameter of the `chr` function can
therefore be annotated with `int | SupportsIndex`.

It seems to me like `SupportsIndex` alone would be enough, since `int`
implements `SupportIndex`, but I chose `int | SupportIndex` to make it
consistent with the annotations on `hex`, `oct` and `bin`.

[implementation]: https://github.com/python/cpython/blob/b05fa90b21dd01bb836285cdd41920320b09e681/Python/bltinmodule.c#L725
[PyLong_AsLongAndOverflow]: https://docs.python.org/3.13/c-api/long.html#c.PyLong_AsLongAndOverflow

Author: sharkdp

stdlib/builtins.pyi

@@ -1295,7 +1295,7 @@ def ascii(obj: object, /) -> str: ...
 def bin(number: int | SupportsIndex, /) -> str: ...
 def breakpoint(*args: Any, **kws: Any) -> None: ...
 def callable(obj: object, /) -> TypeIs[Callable[..., object]]: ...
-def chr(i: int, /) -> str: ...
+def chr(i: int | SupportsIndex, /) -> str: ...
 
 # We define this here instead of using os.PathLike to avoid import cycle issues.
 # See https://github.com/python/typeshed/pull/991#issuecomment-288160993