Add tests for scala3 enum derivation and fix writer derivation for scala3 enums

[Alexxand]

Add tests and fix bugs for #177
Should be merged after #177 .

Tests for simple and parametrized enums:

• semiauto derivation
• semiauto derivation with discriminator
• auto derivation

Bug:
Behaviour of derived writer before this pr (the same for parametrised enum):
SimpleEnum.ONE -> { "ONE" }
SimpleEnum.ONE (with discriminator) -> { "ONE", "__type": "ONE" }
Behaviour of derived writer after this pr (the same for parametrised enum):
SimpleEnum.ONE -> "ONE"
SimpleEnum.ONE (with discriminator) -> { "__type": "ONE" }

Behaviour of reader derivation was not changed.
Derived reader works like "ONE" -> SimpleEnum.ONE (the same for parametrised enum)

However if you will try to use JsonWriter.obj for enum values, but not for the enum itself, like:

implicit val oneWriter: JsonObjectWriter[SimpleEnum.ONE.type] = JsonWriter.obj[SimpleEnum.ONE.type].addField("type")(_ => "ONE")  
implicit val twoWriter: JsonObjectWriter[SimpleEnum.TWO.type] = JsonWriter.obj[SimpleEnum.TWO.type].addField("type")(_ => "TWO")  
implicit val simpleEnumWriter: JsonWriter[SimpleEnum] = jsonWriter[SimpleEnum]

in version after this pr it will produce "type": "ONE" or "type": "TWO" without object start and object end
(in version before this pr it would produce {"type": "ONE"} or {"type": "TWO"})

But you can use JsonWriter.obj for just SimpleEnum, not for its values:

implicit val simpleEnumWriter: JsonWriter[SimpleEnum] = JsonWriter[SimpleEnum].addField("type")(_.toString)

and get the correct behaviour of such writer: SimpleEnum.ONE -> {"type": "ONE"}