docs: ML Inference examples missing error handling

[Saiful-15931]

Problem

The ML Inference docs show basic examples but
don't include any error handling.

For a blockchain app where real money is involved,
new developers need to know how to handle:

• Network failures
• Invalid model CID
• Insufficient wallet balance
• Timeout errors

Suggested Fix

Add a try/except example showing proper error handling:

try:
    result = alpha.infer(
        model_cid='QmbUqS93...',
        model_input={...},
        inference_mode=og.InferenceMode.VANILLA
    )
except Exception as e:
    print(f"Inference failed: {e}")
This would help new developers debug issues faster.