Function matches_email 

pub fn matches_email(pattern: &str, email: &str) -> bool

Check whether a certificate rfc822Name SAN matches an email address.

RFC 6125 Section 6.4.4 / RFC 5280 Section 4.2.1.6:

• The local-part (before @) is case-sensitive per RFC 5321.
• The domain-part (after @) is case-insensitive.
• If the pattern is a bare domain (no @), it matches any email address at that domain.