Use Display trait for Not, AlwaysTrue, and AlwaysFalse

Previously the `VerificationMessage` for `Not`, `AlwaysTrue` and
`AlwaysFalse` were using the `VerificationOutput::value` to populate the
message, but now the `Display` implementation for these is used to
populate the message.

verifier/src/lib.rs

@@ -319,8 +319,8 @@ impl<O> NotOutput<O> {
     }
 }
 
-/// Will negate the output of the [`Verifier::verify()`] operation.
-#[derive(Debug)]
+/// Negated due to `Not`
+#[derive(displaydoc::Display, Debug)]
 pub struct Not<V> {
     verifier: V,
 }
@@ -350,19 +350,20 @@ impl<O, V: VerificationMessage<O>> VerificationMessage<NotOutput<O>> for Not<V>
     ) -> core::fmt::Result {
         let status = choice_to_status_message(result.is_success());
 
-        write!(f, "{:pad$}{status} Negated due to `Not`:", "")?;
+        write!(f, "{:pad$}{status} {self}:", "")?;
         let pad = pad + MESSAGE_INDENT;
         writeln!(f)?;
         self.verifier.fmt_padded(f, pad, &result.value.inner)
     }
 }
 
-/// Success due to `AlwaysTrue`
-#[derive(displaydoc::Display, Clone, Debug, Eq, Hash, PartialEq)]
+/// Marker struct to ensure a node in the `VerificationOutput` was for an
+/// `AlwaysTrue`
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct AlwaysTrueValue;
 
-/// Will always succeed for the [`Verifier::verify()`] operation.
-#[derive(Clone, Debug, Eq, Hash, PartialEq, Default)]
+/// Success due to `AlwaysTrue`
+#[derive(displaydoc::Display, Clone, Debug, Eq, Hash, PartialEq, Default)]
 pub struct AlwaysTrue;
 
 impl<E> Verifier<E> for AlwaysTrue {
@@ -377,20 +378,20 @@ impl VerificationMessage<AlwaysTrueValue> for AlwaysTrue {
         &self,
         f: &mut Formatter<'_>,
         pad: usize,
-        result: &VerificationOutput<AlwaysTrueValue>,
+        _result: &VerificationOutput<AlwaysTrueValue>,
     ) -> core::fmt::Result {
         let status = SUCCESS_MESSAGE_INDICATOR;
-        let value = &result.value;
-        write!(f, "{:pad$}{status} {value}", "")
+        write!(f, "{:pad$}{status} {self}", "")
     }
 }
 
-/// Failure due to `AlwaysFalse`
-#[derive(displaydoc::Display, Clone, Debug, Eq, Hash, PartialEq)]
+/// Marker struct to ensure a node in the `VerificationOutput` was for an
+/// `AlwaysFalse`
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct AlwaysFalseValue;
 
-/// Will always fail for the [`Verifier::verify()`] operation.
-#[derive(Clone, Debug, Eq, Hash, PartialEq, Default)]
+/// Failure due to `AlwaysFalse`
+#[derive(displaydoc::Display, Clone, Debug, Eq, Hash, PartialEq, Default)]
 pub struct AlwaysFalse;
 
 impl<E> Verifier<E> for AlwaysFalse {
@@ -405,11 +406,10 @@ impl VerificationMessage<AlwaysFalseValue> for AlwaysFalse {
         &self,
         f: &mut Formatter<'_>,
         pad: usize,
-        result: &VerificationOutput<AlwaysFalseValue>,
+        _result: &VerificationOutput<AlwaysFalseValue>,
     ) -> core::fmt::Result {
         let status = FAILURE_MESSAGE_INDICATOR;
-        let value = &result.value;
-        write!(f, "{:pad$}{status} {value}", "")
+        write!(f, "{:pad$}{status} {self}", "")
     }
 }