Fix a bug where if some options don't exist on a library it fails to deserialise it causing a crash

[wolffshots]

This pull request includes several updates to the audiobookshelf custom component. The most important changes involve updating the version, adjusting type annotations, and modifying class attributes to support None values.

Version Updates:

• custom_components/audiobookshelf/const.py: Updated VERSION to "v0.2.3".
• custom_components/audiobookshelf/manifest.json: Updated version to "0.2.3".

Type Annotation and Attribute Modifications:

• custom_components/audiobookshelf/sensor.py: Modified full_path attribute in LibraryFolder class to support None values.
• custom_components/audiobookshelf/sensor.py: Modified audiobooks_only attribute in LibrarySettings class to support None values.
• custom_components/audiobookshelf/sensor.py: Modified media_type and settings attributes in Library class to support None values.