Use `Self::Foo` instead of importing variants with wildcard

[tcharding]

We have a ton of cases where we bring error variants into scope using use FooError::*;.

This was done so the pattern match is more terse, especially because error types can have long names. The same goal can be better achieved by using Self::Foo when matching.

The main benefit is that its more clear because for example FooError::Address leads to a bare Address in the pattern match which can be misleading at first glance.

Probably only worth doing if it can be done with AI because otherwise its a ton of work.

[tcharding]

Apologies @jamillambert for not noticing earlier, I tab through the error stuff when reviewing with only a cursory glance - my bad.

[jamillambert]

Before I try to fix this, is it in the Error implementation? I can't find any other relevant occurrences of Error::*

e.g.

impl fmt::Display for ScriptPubkeyError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        use ScriptPubkeyError::*;
        match *self {
            Hex(ref e) => write_err!(f, "conversion of the `hex` field failed"; e),
            Address(ref e) => write_err!(f, "conversion of the `address` field failed"; e),
            Addresses(ref e) => write_err!(f, "conversion of the `addresses` field failed"; e),
        }
    }
}

Should be:

impl fmt::Display for ScriptPubkeyError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            ScriptPubkeyError::Hex(ref e) => write_err!(f, "conversion of the `hex` field failed"; e),
            ScriptPubkeyError::Address(ref e) => write_err!(f, "conversion of the `address` field failed"; e),
            ScriptPubkeyError::Addresses(ref e) => write_err!(f, "conversion of the `addresses` field failed"; e),
        }
    }
}

[tcharding]

Should be like this:

impl fmt::Display for ScriptPubkeyError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Self::Hex(ref e) => write_err!(f, "conversion of the `hex` field failed"; e),
            Self::Address(ref e) => write_err!(f, "conversion of the `address` field failed"; e),
            Self::Addresses(ref e) => write_err!(f, "conversion of the `addresses` field failed"; e),
        }
    }
}

You may see around the place the old style I used to favour

impl fmt::Display for ScriptPubkeyError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        use ScriptPubkeyError as E;
        match *self {
            E::Hex(ref e) => write_err!(f, "conversion of the `hex` field failed"; e),
            E::Address(ref e) => write_err!(f, "conversion of the `address` field failed"; e),
            E::Addresses(ref e) => write_err!(f, "conversion of the `addresses` field failed"; e),
        }
    }
}