better encoding of enote (shorter cashuB)

"V4 tokens are a space-efficient way of serializing tokens using the CBOR binary format. All field are single characters and hex strings are encoded in binary. V4 tokens can only hold proofs from a single mint."

https://cashubtc.github.io/nuts/00/#v4-tokens

The Cashu library is defaulting to the shorter V4 (cashuB) format now, so it’s safe to say cashuA is being phased out. 🫡

https://github.com/cashubtc/cashu-ts/releases/tag/v2.0.0