Generalize Axes __repr__ to 3D

[scottshambaugh]

PR Summary

Axes3D did not have the zlabel included in its repr, this adds that. We could cut down on code duplication by modifying the base axes string, but that seems a little sketchy.

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• [n/a] New features are documented, with examples if plot related.
• [n/a] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• [n/a] API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• [n/a] Documentation is sphinx and numpydoc compliant (the docs should build without error).

[oscargus]

Makes sense. A test would be nice and useful. Especially if one is trying to merge things later.

[anntzer]

I would suggest just writing the base class __repr__ as something like (untested)

        for name, axis in self._axis_map:
            if axis.get_label():
                fields += [f"{name}label={axis.get_label().get_text()!r}"]

[scottshambaugh]

@anntzer that's way nicer, changed

[scottshambaugh]

Tests added