[confidential] Need to encrypt/decrypt Usage for the proxy

[jorgeantonio21]

Otherwise, the usage is passed on clear to the OS. We have two ways to proceed:

[ ] - Add encryption/decryption for Usage which implies having to add this functionality on the proxy as well.
[ ] - The TEE node generates (ideally deterministically) its Sui private key, which is never exposed to the OS. In this case, within the secure enclave, the node signs the usage and sends the signature + hash to the proxy for verification.

I am more inclined on the second option atm.