bugfix: convert non-.wav/.raw files to .wav before passing to pydub

[behackl]

Ongoing post-pyav refactor: fixes #3831

• cleanup inconsistently named containers/streams in added code
• think about actually opening file to check codec
• deal with files that have mulitple audio streams? (try whether this actually works currently)
• maybe add a test?

[behackl]

I've cleaned up the re-encoding of non-wav/raw files, made sure the solution also works with multiple audio channels, and added a test. Ready to be reviewed!

The test uses the manim_caplog fixture introduced in #3680, so it will only pass after that PR is merged.

[JasonGrace2282]

LGTM