Backport of #818 to 12.3

[philipr-za]

A backport of #818 to the 12.3 branch

[apoelstra]

In b6593d6:

I'm struggling to understand this commit. It seems like it just changes an error type from Infallible to () without actually changing anything, but it's labeled as "backporting a unit test".

[apoelstra]

1874266 looks good otherwise

[philipr-za]

In b6593d6:

I'm struggling to understand this commit. It seems like it just changes an error type from Infallible to () without actually changing anything, but it's labeled as "backporting a unit test".

The main change was actually going from the

    type TargetPk = DefiniteDescriptorKey;
    type Error = core::convert::Infallible;

back to the generics of impl Translator<bitcoin::PublicKey, DefiniteDescriptorKey, ()> for TranslateFullPk {

I went from Infallible to () just to be consistent with all the other Translator impl's in the 12.3 branch.

There was also a cargo fmt effect because of that change.

[apoelstra]

Ohh, I see, you're modifying tests that you just added in the previous commit.

Please squash these commits. Otherwise the first one won't compile.