Optional IHistoryTransform added to ChatSession.InitializeSessionFromHistoryAsync

[Norne9]

This pull request introduces an optional parameter, IHistoryTransform? transform, to the InitializeSessionFromHistoryAsync method in the ChatSession class. This change accommodates models that require specific formatting of the chat history.

Some language models may require the chat history to be formatted in a specific way before being passed to the model for generating a response. The addition of the IHistoryTransform parameter allows for the flexibility to apply custom transformations to the chat history when initializing a new session.

This change maintains backward compatibility with existing code that does not provide a custom history transform by making the transform parameter optional and defaulting it to null.