Move layout metrics into theme and apply audit cleanups

crates/core/src/slider.rs

@@ -79,12 +79,6 @@ impl Slider {
         self
     }
 
-    /// Sets the current value; the slider never owns it.
-    pub fn value(mut self, value: f32) -> Self {
-        self.value = value;
-        self
-    }
-
     /// Renders the slider inert, unfocusable, and dimmed; disabled always wins.
     pub fn disabled(mut self, disabled: bool) -> Self {
         self.disabled = disabled;