One signature line of a note:
— <key name> base64(32-bit key ID || signature)
The em dash is U+2014. The base64 blob decodes to the 4-byte big-endian key ID followed by the algorithm-specific signature bytes.
@type t() :: %SignedNote.Signature{ key_id: <<_::4*8>>, name: String.t(), signature: binary() }