This pull request introduces a new ChannelId model to better represent channel identifiers (including sub-channels), improves type safety, and ensures consistency between the channel_id and related productInfo entities. It also introduces a formal enumeration for entity types and adds a dedicated ProductInfo entity. These changes enhance the clarity, maintainability, and correctness of the activity modeling code.

Channel ID and Product Info Enhancements:

• Introduced a new ChannelId model in channel_id.py to represent channel identifiers with optional sub-channels, including custom parsing, serialization, and equality logic.
• Updated the Activity and ConversationReference models to use the new ChannelId type instead of a plain string, including migration logic and backward compatibility handling. [1] [2] [3] [4] [5]
• Implemented logic in Activity to synchronize the channel_id.sub_channel with the ProductInfo entity's id, ensuring data consistency during validation and serialization. [1] [2]

Entity Type Improvements:

• Added a formal EntityTypes enumeration using strenum for well-known entity types, and refactored code to use this enum for clarity and maintainability. [1] [2] [3] [4] [5]

Product Info Entity:

• Introduced a dedicated ProductInfo entity class to model product information within activities, and registered it in the public API. [1] [2] [3] [4] [5]

Dependency Update:

• Added strenum as a dependency to support the new EntityTypes enumeration.

Public API Updates:

• Updated __init__.py files to export the new ChannelId, EntityTypes, and ProductInfo classes, making them available for external use. [1] [2] [3] [4] [5] [6]