Function validate_currency_code 

pub fn validate_currency_code(code: &str) -> Result<()>

Validate a currency code (ISO 4217 format)

Currency codes must be exactly 3 uppercase letters.

Example

use stateset_core::validate_currency_code;

assert!(validate_currency_code("USD").is_ok());
assert!(validate_currency_code("EUR").is_ok());
assert!(validate_currency_code("usd").is_err()); // lowercase
assert!(validate_currency_code("US").is_err()); // too short
assert!(validate_currency_code("USDD").is_err()); // too long