Add HoldLayer button

src/button.rs

@@ -22,7 +22,7 @@ impl From<Modifier> for u8 {
     }
 }
 
-#[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 #[non_exhaustive]
 pub enum Button {
     Mod(Modifier),
@@ -31,6 +31,7 @@ pub enum Button {
     Compose(Key, Key, Option<Key>),
     NextLayer,
     PrevLayer,
+    HoldLayer(u16),
     None,
 }
 
@@ -44,6 +45,7 @@ impl Display for Button {
             Button::Compose(k1, k2, Some(k3)) => write!(f, "⎄ {k1:?} {k2:?} {k3:?}"),
             Button::NextLayer => write!(f, "↘"),
             Button::PrevLayer => write!(f, "↖"),
+            Button::HoldLayer(layer) => write!(f, "HL{layer}"),
             Button::None => write!(f, "Ø"),
         }
     }