Backport unit test from rust-bitcoin#818

Author: philipr-za

src/descriptor/mod.rs

@@ -2073,19 +2073,13 @@ pk(03f28773c2d975288bc7d1d205c3748651b075fbc6610e58cddeeddf8f19405aa8))";
 
         struct TranslateFullPk;
 
-        impl Translator<bitcoin::PublicKey> for TranslateFullPk {
-            type TargetPk = DefiniteDescriptorKey;
-            type Error = core::convert::Infallible;
-
-            fn pk(
-                &mut self,
-                pk: &bitcoin::PublicKey,
-            ) -> Result<DefiniteDescriptorKey, Self::Error> {
+        impl Translator<bitcoin::PublicKey, DefiniteDescriptorKey, ()> for TranslateFullPk {
+            fn pk(&mut self, pk: &bitcoin::PublicKey) -> Result<DefiniteDescriptorKey, ()> {
                 Ok(DefiniteDescriptorKey::new(DescriptorPublicKey::from(*pk))
                     .expect("DescriptorPublicKey from PublicKey has no wildcards"))
             }
 
-            translate_hash_clone!(bitcoin::PublicKey, DefiniteDescriptorKey, Self::Error);
+            translate_hash_clone!(bitcoin::PublicKey, DefiniteDescriptorKey, ());
         }
 
         let converted_descriptor = full_pk_descriptor
@@ -2100,16 +2094,13 @@ pk(03f28773c2d975288bc7d1d205c3748651b075fbc6610e58cddeeddf8f19405aa8))";
 
         struct TranslateXOnlyPk;
 
-        impl Translator<XOnlyPublicKey> for TranslateXOnlyPk {
-            type TargetPk = DefiniteDescriptorKey;
-            type Error = core::convert::Infallible;
-
-            fn pk(&mut self, pk: &XOnlyPublicKey) -> Result<DefiniteDescriptorKey, Self::Error> {
+        impl Translator<XOnlyPublicKey, DefiniteDescriptorKey, ()> for TranslateXOnlyPk {
+            fn pk(&mut self, pk: &XOnlyPublicKey) -> Result<DefiniteDescriptorKey, ()> {
                 Ok(DefiniteDescriptorKey::new(DescriptorPublicKey::from(*pk))
                     .expect("DescriptorPublicKey from XOnlyPublicKey has no wildcards"))
             }
 
-            translate_hash_clone!(XOnlyPublicKey, DefiniteDescriptorKey, Self::Error);
+            translate_hash_clone!(XOnlyPublicKey, DefiniteDescriptorKey, ());
         }
 
         let xonly_converted_descriptor = xonly_pk_descriptor