Handle bytes/bytearray return values explicitly

[bbopen]

Summary

Returning Python bytes/bytearray currently leads to JSON serialization failures; these should be encoded or rejected explicitly.

Failure mode

• json.dumps raises TypeError: Object of type bytes is not JSON serializable.
• The error can surface as a protocol error rather than a clear codec error.

Repro (adversarial)

• Add a fixture that returns b"\x00\x01" and bytearray([...]).
• Call through NodeBridge and assert explicit error or base64 envelope.

Acceptance criteria

• Bytes/bytearray are either encoded in a dedicated envelope (preferred) or rejected with a clear error.
• Adversarial tests cover bytes/bytearray return paths.

[bbopen]

Fixed in PR #153: SafeCodec handles bytes/bytearray via configurable bytesHandling option (default: 'base64'). Binary data is encoded with tywrap_bytes marker and b64 field.