Make method main actor

Paralayout/GeometryAdditions.swift

@@ -155,6 +155,7 @@ extension CGRect {
  /// - parameter amount: The size of the slice (absolute).
  /// - returns: A tuple (slice: A rect with a width/height of the `amount`, remainder: A rect with a width/height of
  /// the receiver reduced by `amount`).
+ @MainActor
  public func slice(
  from edge: DirectionalEdge,
  amount: CGFloat,