Re-arrange source code and tests

Sources/SwiftUIMath/Internal/Syntax/Atoms/Space.swift

@@ -0,0 +1,17 @@
+import Foundation
+
+extension Math {
+  final class Space: Atom {
+    var amount: CGFloat
+
+    init(_ space: Space) {
+      self.amount = space.amount
+      super.init(space)
+    }
+
+    init(amount: CGFloat = 0) {
+      self.amount = amount
+      super.init(type: .space)
+    }
+  }
+}