Fix ClassCastException for hierarchical enum JSON encoding

[SolariSystems]

Fixes #668

Problem

When using JSON codec with auto-derived schemas for hierarchical sealed trait enums (e.g., Animal > Mammal > Bison), encoding fails with ClassCastException: Schema$Enum1 cannot be cast to Schema$CaseClass0.

Root Cause

The JsonCodec implementation incorrectly assumed all enum cases have CaseClass0 schemas. However, intermediate sealed traits in hierarchical enums have Enum schemas, not CaseClass0.

Solution

• Added constructEnumCase helper function that pattern matches on case schema type
• Handles both CaseClass0 and Enum case schemas correctly
• Uses the proper Case.construct method for type-safe construction
• Updated three locations in JsonCodec.scala that made the incorrect assumption

Changes

• zio-schema-json/shared/src/main/scala/zio/schema/codec/JsonCodec.scala: Fix + helper function
• zio-schema-json/shared/src/test/scala/zio/schema/codec/JsonCodecSpec668.scala: Regression tests

Testing

Added regression test suite covering:

• Simple hierarchical enum (Animal > Mammal > Bison)
• Deeper hierarchy (Vehicle > LandVehicle > Car > Sedan)
• Round-trip encoding/decoding

CI will validate compilation and test suite passes.

[plokhotnyuk]

You made non-needed changes by replacing toArray in other places. Also, the constructEnumCase should be just private (not package private). And you have pushed all that in a wrong branch: https://github.com/zio/zio-schema/pull/967/changes/3b6f9ed649563fa9985c05bcc88d8b55d8bfac83

[plokhotnyuk]

@SolariSystems Please use more advanced ADT with leaf classes on different levels of hierarchy in tests.

One of real-word ADTs that could be reused for tests is this GeoJSON hierarchy