Function format_rate 

pub fn format_rate(hundredths: i64, decimal_places: usize) -> String

Format a rate stored as hundredths of a percent to a decimal string.

For example, 1800 (= 18%) with 4 decimal places → "18.0000".

Examples

use fiscal_core::format_utils::format_rate;
assert_eq!(format_rate(1800, 4), "18.0000");
assert_eq!(format_rate(750, 2), "7.50");