Implement `Display` for `HumanReadableName`

[tnull]

We have HumanReadableName::from_encoded to read the object from the default BIP353 encoding. However, we don't provide a convenient conterpart. We should implement Display for HumanReadableName, that allows printing as ₿user@domain.

(cc @chuksys)

[chuksys]

Would like to pick this up.