Implement and use the AES cipher instead of PoseidonCipher

[xevisalle]

Epic

Summary

Atm we were using PoseidonCipher to encrypt the value / blinder in the notes. While it was a requirement for in-circuit encryption, this is not the case anymore as we got rid of the send to contract obfuscated approach. We can now use a faster solution instead, like AES. In particular, we've chosen AES-GCM (https://crates.io/crates/aes-gcm), given that:

• it's efficient
• it's approved by NIST
• the crate has been audited
• the crate is widely used