Changelog:

• fix issue in Scala 2 related to (probably?) Symbol initialization AND default values in constructor not relying on companion apply (#562, fixed in #563)
• improve support for singleton types - case objects and Scala 3 enums as target should always succeed and always be available as a fallback values for parameters (do not require matching input parameter) (#407, fixed in #559)
• add Cats instances (Category/Invariant) for bi-directional transformations (Codec/Iso) (#566)
• improve docs testing - test whether the Scala CLI output printed with pprint matches the expectation (#536, fixed in #567)
• improve Protobufs support for data types modeled using sealed traits:
  • implicit with automatic handling of Empty oneof for sealed_value
  • implicit with automatic handling of Unrecognized for enum
  • ability to automatically unwrap non-AnyVal value type (enabled with a flag) which can be used to unwrap oneof values (#531, fixed in #568)