Fix LateInitializationError in Llama dispose method

[Anees004]

This commit fixes a critical bug that causes LateInitializationError when the Llama constructor fails during initialization.

Problem:

• dispose() method is called during constructor failure
• dispose() tries to access uninitialized late fields
• Results in LateInitializationError crash

Solution:

• Add _isInitialized flag to track initialization state
• Only access late fields in dispose() when initialization is complete
• Add try-catch around batch.free() for additional safety
• Ensure batch is always initialized to prevent null reference errors

Testing:

• Verified fix prevents crashes
• Maintains backward compatibility
• Allows graceful fallback to mock mode

[Anees004]

LateInitializationError error fix