fix(mlc-llm): fix mlc-llm ChatModuleClient with MLCEngine

[zhaohan-dong]

Fix on issue #1206.
Both mlc_chat and ChatModule are depreciated. Replaced with MLCEngine which will be suppoorted going forward.
A few considerations:

• Renaming the class to reflect the change from ChatModule
• Use EngineConfig when setting up the MLCEngine to have more control over configuration

[arnavsinghvi11]

Thanks @zhaohan-dong !