Add optional `orjson` backend and `to_json_bytes` / `from_json_bytes` helpers

[rnag]

• Goal: Faster JSON serialization + bytes I/O path.

• Scope:

  • Optional extra: dataclass-wizard[orjson]
  • formats.json.dumps(..., backend="orjson") -> bytes (or separate dumps_bytes)
  • DataclassWizard.to_json_bytes() / DataclassWizard.from_json_bytes() (optional)

• Acceptance criteria:

  • No required dependency changes for core users.
  • Clear behavior for bytes vs str.
  • Benchmarks or at least microbench + docs note.