I'm using the swift-sodium library and need a 32 bytes long UInt8 array (public key) to seal a message. However, the public key which is generated by the tweetnacl-js library that I got from an api is a 44 bytes long base64 string. How do I convert the 44 bytes long base64 public key to a 32 bytes long UInt8 array so I can pass it to the seal function?