Add display model

Sources/SwiftUIMath/Internal/Display/DisplayRadical.swift

@@ -0,0 +1,34 @@
+import CoreGraphics
+import Foundation
+
+extension Math {
+  final class DisplayRadical: DisplayNode {
+    var radicand: DisplayList?
+    var degree: DisplayList?
+    var radicalGlyph: DisplayNode?
+
+    var radicalShift: CGFloat = 0
+    var topKern: CGFloat = 0
+    var lineThickness: CGFloat = 0
+
+    init(radicand: DisplayList?, glyph: DisplayNode, position: CGPoint, range: NSRange) {
+      self.radicand = radicand
+      self.radicalGlyph = glyph
+      super.init()
+      self.position = position
+      self.range = range
+    }
+
+    override var position: CGPoint {
+      didSet { updateRadicandPosition() }
+    }
+
+    func updateRadicandPosition() {
+      guard let radicand, let radicalGlyph else { return }
+      radicand.position = CGPoint(
+        x: position.x + radicalShift + radicalGlyph.width,
+        y: position.y
+      )
+    }
+  }
+}