Add more graphical snapshot tests

[IndrajeetPatil]

Creating an issue just in case if there are newcomers who wish to learn how to write such tests and contribute to {see} in doing so.

You can have a look at these slides on how to write such tests: https://indrajeetpatil.github.io/intro-to-snapshot-testing/

[strengejacke]

We should pin this post.

[ANAMASGARD]

@IndrajeetPatil @strengejacke @rempsyc I have raised a PR can please review it and give your feedback ! I've added 18 vdiffr tests that cover the main check_model() plots and their variations. These should catch any visual regressions in future updates.

https://github.com/easystats/see/pull/423