Update codecov/codecov-action action to v6

Bump version to 4.0.2

[mkvfontvalidator] Log warning if the mkv doesn't contain .ass file

[mkvextract] Don't run mkvextract if the mkv doesn't contain ass files

[mkvextract] Don't run mkvextract if the mkv doesn't contain font files

[README] Add pipx installation advice

Bump version to 4.0.1

[__main__] Add the file_handler to the root logger

Bump version to 4.0.0

Update dependency python to 3.14

Remove trailing whitespace

Bump dependencies that support Python 3.14

Sort the import with isort

Remove unused imports with autoflake

Use PyUpgrade to upgrade to Python 3.10 syntax