Enhance generateContentStream with streamCallbacks support. Fixes #322 #401

[demoncoder-crypto]

Add streamCallbacks to generateContentStream

Changes

• Added a StreamCallbacks interface with onData and onDone callback functions
• Updated generateContentStream to accept and process the callbacks

Example Usage

await model.generateContentStream("Tell me a joke", {}, {
  onData: (chunk) => process.stdout.write(chunk),  
  onDone: (fullText) => console.log("\nFinal output:", fullText),
});

Testing

The changes have been tested with both unit tests and manual validation.

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