yoda: warning cleanup sweep (dead code + clippy --fix) (squashed)

Squash of 4 yoda commits:
- 84437e21 yoda: libcosmic-yoda dead-code purge (14->0 warnings)
- 999db0a4 yoda: cosmic-theme cleanup (4->0 warnings) — workspace at 0 warnings total
- 4743bb8e yoda: cargo clippy --fix on libcosmic-yoda (115->33 warnings)
- 675f3b59 chore: reduce local stack warnings

src/theme/style/iced.rs

@@ -170,18 +170,15 @@ impl Button {
  * TODO: Checkbox
  */
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Default)]
 pub enum Checkbox {
+    #[default]
     Primary,
     Secondary,
     Success,
     Danger,
 }
 
-impl Default for Checkbox {
-    fn default() -> Self {
-        Self::Primary
-    }
-}
 
 impl iced_checkbox::Catalog for Theme {
     type Class<'a> = Checkbox;
@@ -1192,7 +1189,7 @@ impl scrollable::Catalog for Theme {
                         background: Color::TRANSPARENT.into(),
                         border: Border::default(),
                         shadow: Shadow::default(),
-                        icon: Color::TRANSPARENT.into(),
+                        icon: Color::TRANSPARENT,
                     },
                 };
                 let small_widget_container = self.current_container().small_widget.with_alpha(0.7);
@@ -1260,7 +1257,7 @@ impl scrollable::Catalog for Theme {
                         background: Color::TRANSPARENT.into(),
                         border: Border::default(),
                         shadow: Shadow::default(),
-                        icon: Color::TRANSPARENT.into(),
+                        icon: Color::TRANSPARENT,
                     },
                 };