CSSUTILS logger overrides existing config on import

Hi!

On first import of `cssutils`, the `'CSSUTILS'` logger is set up and configured with some default values, as can be seen here:
https://github.com/jaraco/cssutils/blob/main/cssutils/errorhandler.py#L51-L56

This can lead to issues if your import of `cssutils` happens later than your main logging config setup, since it will override whatever is already configured. To avoid it, you must pre-emptively import `cssutils` before your own logging config.

It would be easier if `cssutils` detected if the logger has already been set up, and didn't add it's own default config in that case. At the very least, if it preserved the loglevel the user has selected that would help.

Lies cssutils/errorhandler.py in den Zeilen 51–56 und verfolge, wie der CSSUTILS-Logger beim ersten Import konfiguriert wird. Definiere „done“ als das Beibehalten einer vorhandenen Logger-Konfiguration, einschließlich des Log-Levels des Benutzers, anstatt Defaults anzuwenden; das Issue nennt keine Testdatei, also ermittle vor den Änderungen die relevante vorhandene Testabdeckung.

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