Function postgres_in_pattern 

pub fn postgres_in_pattern(start_idx: usize, count: usize) -> String

Get a pre-computed PostgreSQL IN placeholder pattern. Returns patterns like “$1, $2, $3” for count=3 starting at start_idx=1.

For counts 1-10 with start_idx=1, returns a pre-computed static string. For other cases, dynamically generates the pattern.