Support for Fine-tuning APIs

[krishnaagrawal7508]

What was changed?

• Implemented fine-tuning support in the Node.js SDK for the Gemini API.
• Added new methods for fine-tuning inside the GenerativeModel class.
• Added method to listTunedModels(): Lists all tuned models.
• Added method to createTunedModel(): Creates a new tuned model using a dataset.
• Added method to checkTuningStatus(): Checks the status of an ongoing fine-tuning job.
• Added method to deleteTunedModel(): Deletes a tuned model.
• Introduced a new fine-tuning helper module in methods/fine-tuning.ts that handles API requests for fine-tuning.
• Updated unit tests in generative-model.test.ts to cover fine-tuning methods using sinon stubs.

How was this tested?

Added unit tests for fine-tuning API calls using sinon stubs to mock API responses.