unit tests update

[Hirogen]

This pull request improves backward compatibility handling for legacy JSON property names in the settings and preferences classes, ensuring that obsolete properties are correctly ignored during serialization and do not cause issues when loading or saving configuration files. It also introduces comprehensive tests to verify correct behavior with old and mixed-format data.

Backward compatibility improvements:

• Updated obsolete properties (HilightGroupList and HilightEntryList) in Preferences, Settings, and HighlightGroup to ensure they are ignored by System.Text.Json during serialization, and configured Newtonsoft.Json to ignore default/null values. These properties now always return null to prevent accidental serialization. [1] [2] [3] [4]

Testing enhancements:

• Added new tests in ConfigManagerTest.cs to verify:
  • Legacy JSON with the old hilightGroupList typo loads correctly into the new property.
  • Saving as JSON does not write obsolete property names.
  • Loading JSON with both new and old property names does not create duplicate entries.