"Expires" is calculated using a double with three decimals: - [Signatures.java](https://github.com/tomitribe/http-signatures-java/blob/master/src/main/java/org/tomitribe/auth/signatures/Signatures.java#L90) [RFC](https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-12#section-2.1.5) states this for "expires": ` The value MUST be a Unix timestamp integer value` Why the value is calculated using a double?