Function domain_prefix_to_field 

pub(crate) fn domain_prefix_to_field<F: PrimeField>(prefix: String) -> F

Transform domain prefix string to field element.

The prefix must be at most 20 characters. Shorter strings are right-padded with asterisks (*) to reach 20 characters before conversion to a field element. For example, "CodaSignature" becomes "CodaSignature*******".