Improve protobuf support for sealed

[MateuszKubuszok]

• [x] refactor tests
• [x] add implicit handling empty GeneratedSealedOneOf
  • [ ] fix Scala 3 issue ( https://github.com/scala/scala3/issues/21122 :/)
• [x] add implicit handling empty GeneratedEnum
• [x] add flag allowing to handle non-AnyVal wrappers automatically
  • [x] tests
  • [x] docs

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.65217% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.05%. Comparing base (515fe41) to head (999b3c9).

Files	Patch %	Lines
...io/scalaland/chimney/dsl/TransformerFlagsDsl.scala	50.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #568 +/- ## ========================================== + Coverage 87.88% 88.05% +0.17% ========================================== Files 153 153 Lines 5910 5911 +1 Branches 474 500 +26 ========================================== + Hits 5194 5205 +11 + Misses 716 706 -10 ```

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