Refactor model

Sources/SwiftUIMath/Internal/Model/Atoms/Radical.swift

@@ -0,0 +1,45 @@
+import Foundation
+
+extension Math {
+  final class Radical: Atom {
+    var radicand: AtomList?
+    var degree: AtomList?
+
+    override var description: String {
+      [
+        "\\sqrt",
+        degree.map { "[\($0)]" },
+        "{\(radicand?.description ?? "placeholder")}",
+        superscript.map { "^{\($0)}" },
+        `subscript`.map { "_{\($0)}" },
+      ]
+      .compactMap(\.self)
+      .joined()
+    }
+
+    override var finalized: Math.Atom {
+      let finalized = super.finalized
+
+      if let radical = finalized as? Radical {
+        radical.radicand = radical.radicand?.finalized
+        radical.degree = radical.degree?.finalized
+      }
+
+      return finalized
+    }
+
+    init(_ radical: Radical) {
+      self.radicand = radical.radicand.map { AtomList($0) }
+      self.degree = radical.degree.map { AtomList($0) }
+
+      super.init(radical)
+    }
+
+    init(radicand: AtomList? = nil, degree: AtomList? = nil) {
+      self.radicand = radicand
+      self.degree = degree
+
+      super.init(type: .radical)
+    }
+  }
+}