Constant APPLICATION_PKCS7_MIME_CERTS_ONLY 

pub const APPLICATION_PKCS7_MIME_CERTS_ONLY: u16 = 281;

application/pkcs7-mime; smime-type=certs-only (RFC 9483 §10.1, TBD281).

Used for CA certificate chain responses (/cacerts, /crts) and enrollment certificate responses.