assign_nested_cm_ids should use next_column_mapping_id

[nicklan]

Today assign_nested_cm_ids does:

*max_id += 1;
nested_ids.insert(element_path.clone(), serde_json::Value::from(*max_id));

If max_id is already at the max int value, we will overflow. next_column_mapping_id exists exactly to solve this problem, we should use that instead of doing the +=1.

[yigitcan-ozturk]

I'd like to work on this. I'll update the nested column-mapping ID allocation to use next_column_mapping_id consistently and add focused regression coverage for the overflow/protocol-limit path.

[nicklan]

@yigitcan-ozturk thanks! please do look at our AI policy to make sure you don't waste tokens and/or our time.