update: new model xlsr

feat: Implement Whisper model preloading during FastAPI startup for optimized performance

Refactor code structure for improved readability and maintainability

Implement Lesson Practice 2 Agent with state management and routing logic; add practice and teaching agent functions; create prompts for conversation and teaching; establish pronunciation API with lesson data and search functionality.

feat: add speaking route for pronunciation assessment API

feat: evaluation when end

Implement lesson practice agent and related functionality

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