Fixed behavior of config.background_opacity < 1 and duplicated log messages

[abul4fia]

Setting background_transparency=0.0 should have the same effect than setting transparent=True. The output format must be compatible with transparency (.mov, .webm). Otherwise ffpmeg fails.

This patch ensures that background_transparency=0.0 triggers the change of the output format. Also a WARNING is raised about the change in the output format.

I want to thank @SirJamesClarkMaxwell for inspiring me to tackle this issue.

Overview: What does this pull request change?

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

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

[JasonGrace2282]

LGTM

[behackl]

Wouldn't actually any value for background_opacity smaller than 1 mean that the video should be rendered with transparency?

[behackl]

I've pushed some fixes for the behavior of config.background_opacity strictly between 0 and 1, and added an explicit test for the case of config.background_opacity == 0.5.

It would be great if someone could cross-review my changes, otherwise I'm happy to get this merged.

[behackl]

I've now properly fixed the logger situation -- sorry, this should probably have been a separate PR. Should be easiest to review by looking at c800ba1 and 78dfd41 separately.

[JasonGrace2282]

Took a look at the changes, mostly looks good to me. I did leave some comments, so I would appreciate if you or @behackl could take a look :)
I also have one question now: with this change, should we just have a per-file logger with logger = logging.getLogger("manim")? If so, would it make sense to remove the logger from being exported in manim._config?

Sidenote:
I was actually having similar problems on experimental so maybe this will help out :)

[JasonGrace2282]

Left one idea - otherwise LGTM!

[JasonGrace2282]

Actually just realized there is a line added that was added in another PR (#3839 )
The other changes look useful, so maybe just merge main into this branch and I'll double check then?

[JasonGrace2282]

Oh nice, I love git :)
LGTM, for real, this time.