feat: add switch control when watching events whether deserialization is required

This PR adds an option to disable automatic deserialization in the Watch stream().
By allowing clients to opt-out of automatic deserialization when only basic
JSON parsing is needed, we can significantly reduce time cost and improve
event processing throughput. This is particularly important in scenarios with
high event volumes or resource constraints.

Key changes:
- Added a 'deserialize' parameter to Watch.stream() method (defaults to True for backward compatibility)
- When deserialize=False, events are only JSON parsed without model conversion
- Maintains the original behavior when deserialize=True
- Added test cases to verify both behaviors