[BUG] Scala 3 remaining issues

[Grifs]

What happened?

The code is well merged into develop now, but there are some open questions/issues:

• Circe can't be higher than 0.14.7 or it breaks the history
• There are some @unchecked annotations for incomplete regex matches, because Scala 3 now checks this
• All encoders & decoders have to be explicitly imported. Seems like it's functionality that wasn't copied to the new version of Circe (previously in circe-generic-extras).
• Empty files are decoded to Json.false instead of a null of the requested class. Some minor checks were added to prevent this from happening, but it's still that's not 100% investigated.
• Some other -feature warnings (quite new, is about implicit conversion methods needing to be explicitly defined).

Steps to reproduce

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Expected behavior

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Relevant log output

No response

Version

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Possible solution

No response

Confirmation

• I have searched the existing issues to make sure this is not a duplicate.
• I have provided clear and concise information about the bug.

Additional context

No response