Summary

Port MessagePack support from ZIO Schema v1 to ZIO Schema 2 in a new top-level schema-messagepack project.

Implementation includes:

• MessagePackBinaryCodec abstract class extending BinaryCodec[A]
• MessagePackFormat object with Deriver[MessagePackBinaryCodec]
• Support for all 30 primitive types (Unit, Boolean, Byte, Short, Int, Long, Float, Double, Char, String, BigInt, BigDecimal, all java.time types, Currency, UUID)
• Record, variant, sequence, map, dynamic value, and wrapper support
• Recursive type support via ThreadLocal cache
• Comprehensive test suite with 78 tests

Deriver Methods Implemented:

• derivePrimitive - All primitive types
• deriveRecord - Case classes encoded as MessagePack maps
• deriveVariant - Sealed traits encoded as single-entry maps
• deriveSequence - Collections encoded as MessagePack arrays
• deriveMap - Maps encoded as MessagePack maps
• deriveDynamic - DynamicValue support
• deriveWrapper - Wrapper types with validation

Test plan

• All 78 tests pass
• Format check passes
• Compiles against latest main

/claim #682