Kotlin JSON Benchmarks

The benchmark harness is in benchmarks/kotlin. It compares Fory JSON Kotlin, kotlinx.serialization, Moshi, and Jackson Kotlin with:

• one immutable MediaContent model with no public zero-argument constructor;
• the Eishay fixture whose SHA-256 is 8faba2f57ab397f319aced5cf1e8411a76785557d4c7d1703ec9d540354310a1;
• String serialization, UTF-8 byte serialization, String deserialization, and UTF-8 byte deserialization for each library;
• one standard JMH invocation for all 16 methods;
• retained declared-type serializers, adapters, readers, and writers prepared outside timing;
• fixture decode, own-output round-trip, and all-output JSON-tree equivalence checks before timing.