There are two issues:

1. We had not "opted" into the custom error messaging for the tests.
2. We have to be careful that we attach the result from compare_image to
the original Compare instance (cmp._err) and not a copy of it.

closes #955

... unless if using labs to overwrite.

closes #960

Previous commit has surface a test that was wrong to begin with.

closes #962

These changes replace `_ipython_display_` with `_repr_mimebundle_`
protocol displaying plots within notebooks. Previously, plotnine used
`_ipython_display_()` for display, which works via side effects and
assumes an IPython/Jupyter environment.

Since IPython 6.1 (May 2017), the `_repr_mimebundle_()` protocol allows
objects to return display data instead of triggering side effects. This
decouples rendering from IPython, letting any compatible frontend (e.g.,
Jupyter, marimo) handle presentation without requiring the object to be
aware of the runtime.

The repr continues to generate a single format (PNG, SVG, etc.) based on
configuration to match prior behavior with the `_ipython_display_`.

References:
- https://ipython.readthedocs.io/en/stable/config/integrating.html
- https://ipython.readthedocs.io/en/stable/api/generated/IPython.core.formatters.html

The previous change made this function an unneccessary.

closes #970

Caused by newer version of pandas-stubs.

The dependencies and checks have some slight drift and a few of these
tests fail.

I think the best solution would involve a lockfile that is associated
with a release.