In the cardano-rosetta construction API what is hex_bytes?

How can I create public keys in the correct format for the rosetta api?

I can use cardano-addresses to create and derive keys and addresses. But I’m confused about their encodings.

The cardano-rosetta (repo) construction endpoints use hex_bytes to represent a public key, but im not sure what this is.

Could someone clarify a bit or link me to some documentation I’ve missed? If we have a valid root private key or mnemonic, what is the preferred way to derive a master public key, and how do we then convert it to a format that can be used by cardano-rosetta (hex_bytes)?