PyAV is blocking the upgrade to Python 3.14

[cclauss]

Description of proposed feature

PyAV v16.0.1 supports Python 3.14, but our GitHub Actions tests fail on that version.

• Pin version of pyav to avoid breaking changes in their API #4037
• Add Python 3.14 to the testing #4493

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• Fix tests to run on Cairo 1.18.0 #3416 @naveen521kk

The file .github/scripts/ci_build_cairo.py will probably fail on Python 3.14 because of the security changes made to:

• https://docs.python.org/3/library/tarfile.html#tarfile.TarFile.extractall

manim/.github/scripts/ci_build_cairo.py

Line 59 in de090c1

file.extractall(directory)

How can the new feature be used?

Additional comments