Use object instead of Any for labels() parameters

[gregoiredx]

I'm working on a project where we try to reduce lines flagged as Any by mypy line precision report.

The type of labels() parameters is Any, reducing the whole line as Any (mypy takes the worst of the line typing for its report).

Using object here looks like the right choice.

From https://mypy.readthedocs.io/en/stable/kinds_of_types.html#the-any-type

This should not be confused with the object type, which represents the set of all values. Unlike object, Any introduces type unsafety — see Any vs. object for more.

I first thought it would even be str since it's the natural type of labels, but labels() transforms parameters to strings automatically (labelvalues = tuple(str(labelkwargs[l]) for l in self._labelnames) and labelvalues = tuple(str(l) for l in labelvalues)).

So we mean "anything that can be stred", object looks like a good candidate for that type.

Note: I had to introduce str_labelvalues to comply with mypy (since now labelvalues has type tuple[object, ...] which is not compatible with tuple[str, ...]).

[gregoiredx]

Hello @csmarchbanks 👋 Following the CONTRIBUTING.md, I should ping you to get your review for a trivial change.

This is just a type change from Any to object. What do you think about it?