Function validate_top_k 

pub fn validate_top_k(top_k: usize) -> Result<usize, VectorError>

M-16 fix: Validate whether top_k is within reasonable range

• top_k = 0: Returns TopKExceeded error (meaningless query)
• top_k > MAX_TOP_K: Returns TopKExceeded error
• 1 <= top_k <= MAX_TOP_K: Returns Ok