ZioJsonDataConverter

Entry point for constructing a DataConverter that uses zio-json for all user-owned payloads. Jackson is deliberately excluded from the chain — zio-temporal is Scala-only and zio-json covers the full encoding surface.

Chain ordering (Temporal's DefaultDataConverter tries each in order):

1. NullPayloadConverter — null values
2. ByteArrayPayloadConverter — raw byte buffers
3. ProtobufJsonPayloadConverter — Temporal-internal protobuf types like WorkflowExecution
4. TemporalInternalsPayloadConverter — an allow-listed set of Temporal Java SDK internal POJOs (currently WorkflowRetryerInternal$SerializableRetryOptions) that leak into the chain via Workflow.retry's mutableSideEffect and for which no user-provided codec exists. The upstream SDK relies on Jackson's reflective fallback here; we substitute a surgical reflective encoder.
5. ZioJsonPayloadConverter encoding json/zio — user-owned payloads; claimed first on encode.
6. ZioJsonPayloadConverter encoding json/plain — decode-only compatibility with recorded workflow histories that were originally written by the Jackson-based DefaultDataConverter. json/plain is just vanilla JSON, so the same registry decodes it correctly. Position matters: on encode, DefaultDataConverter stops at the first converter returning non-empty, so the json/zio instance wins and fresh payloads never get stamped json/plain.