Rename SceneFileWriter.save_final_image() to save_image()

[fmuenkel]

• Rename SceneFileWriter.save_final_image() to save_image() and fix docstring

• fix two type annotations in scene_file_writer.py

• make docstrings consistent

Overview: What does this pull request change?

Motivation and Explanation: Why and how do your changes improve the library?

save_final_image() was incorrectly named. It is simply saving an image at any point during the scene. It is used in cairo_renderer.py and opengl_renderer.py to save the last frame if save_last_frame is set in the configuration.

Links to added or changed documentation pages

Further Information and Comments

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[behackl]

Fine with me, thanks! Will leave open for a bit before merging in case someone else thinks that a deprecation period is necessary.

[chopan050]

Thanks for the change! I agree with it.

There's one detail I want to talk about: