🐛 zv: Do not derive Eq for Signature

As per [`Eq`](https://doc.rust-lang.org/stable/std/cmp/trait.Eq.html#derivable)
docs on deriving: "Note that the derive strategy requires all fields are Eq,
 which isn’t always desired."

We specify conditional `Signature` equality that does not include all
fields are (derivable) `Eq`.

Therefore this manually implements `Eq` for `Signature`.

zvariant/src/signature.rs

@@ -83,7 +83,7 @@ impl<'b> std::ops::Deref for Bytes<'b> {
 ///
 /// [identifies]: https://dbus.freedesktop.org/doc/dbus-specification.html#type-system
 /// [`slice`]: #method.slice
-#[derive(Eq, Hash, Clone)]
+#[derive(Hash, Clone)]
 pub struct Signature<'a> {
     bytes: Bytes<'a>,
     pos: usize,
@@ -392,6 +392,9 @@ impl<'a> PartialEq<&str> for Signature<'a> {
     }
 }
 
+// Do not derive `Eq` if not all fields are `Eq`.
+impl Eq for Signature<'_> {}
+
 impl<'a> Display for Signature<'a> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         std::fmt::Display::fmt(&self.as_str(), f)