to_serializable_dict now skips types not in ALLOWED_DESERIALIZE_TYPES
(returns None), preventing objects like logging.Logger from being
serialized as {"type": "Logger", "params": {...}} which then fails
deserialization. from_serializable_dict returns None for unknown types
instead of raising ValueError, handling payloads from older clients.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
