Refactor MessageState to Use Msg Struct and Simplify Initialization

[deanlee]

Refactors the MessageState class to improve its structure and initialization process:

1. Replaced multiple member variables with a single struct Msg to encapsulate message-related data. These member variables were essentially duplicates of the struct Msg's members.
2. Added a constructor MessageState::MessageState to simplify the initialization process.
3. Updated the code to use the new struct and constructor for better readability and maintainability.

This refactor enhances code clarity, reduces redundancy, and streamlines the initialization process.

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