update build tool to swift 6.1

Author: chenhaiteng

CoreGraphicsExtension.podspec

@@ -11,7 +11,7 @@ Pod::Spec.new do |s|
   s.version          = '0.4.2'
   s.summary          = 'A small libray to provide polar coordinate feature and some convienet extension of CoreGraphics'
 # s.swift_version:begin
-  s.swift_version  = '5.3.0'
+  s.swift_version  = '6.1.0'
   # s.swift_version    = '${SWIFT_VERSION}'
 
 # s.platform:begin

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.3
+// swift-tools-version:6.1
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription

Sources/CoreGraphicsExtension/CGAngle.swift

@@ -11,7 +11,7 @@ import CoreGraphics
 public typealias CGAngle = CGFloat
 
 extension CGAngle {
-    public static var zero: CGFloat = 0.0
+    public static let zero: CGFloat = 0.0
     public var radians: CGFloat {
         self
     }

Sources/CoreGraphicsExtension/CGPolarPoint.swift

@@ -8,8 +8,8 @@
 import Foundation
 import CoreGraphics
 
-public struct CGPolarPoint {
-    public static var zero = CGPolarPoint()
+public struct CGPolarPoint : Sendable {
+    public static let zero = CGPolarPoint()
     public var radius: CGFloat
     public var cgangle: CGAngle
     public var cgpoint: CGPoint