secKeyAlgorithm

Maps a SigningAlgorithm to the corresponding Apple Security framework SecKeyAlgorithm.

Returns null for HMAC algorithms (which use raw CCHmac instead) and for SigningAlgorithm.None.

The *Message* variants are used so the full message is passed and the framework handles hashing internally, matching the contract of co.touchlab.kjwt.processor.JwsSigner.