Update swift-tools-version to 6.2 and swift-syntax to 602.0.0 and fix minor build issues

Author: alschmut

Package.resolved

@@ -1,4 +1,4 @@
-// swift-tools-version: 5.9
+// swift-tools-version: 6.2
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
@@ -11,7 +11,7 @@ let package = Package(
         .library(name: "Buildable", targets: ["Buildable"])
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-syntax.git", .upToNextMajor(from: "510.0.0")),
+        .package(url: "https://github.com/apple/swift-syntax.git", .upToNextMajor(from: "602.0.0")),
     ],
     targets: [
         .macro(

Package.swift

@@ -5,6 +5,7 @@
 //  Created by Alexander Schmutz on 03.07.23.
 //
 
+import Foundation
 import SwiftSyntax
 
 func extractMembersFrom(_ memberBlockItemList: MemberBlockItemListSyntax) -> [StructMember] {

Sources/BuildableMacro/StructAndClass/Helper/ExtractMembers.swift

@@ -65,7 +65,7 @@ private func closureCodeBlock(
     }
 }
 
-private var mapping: [String: ExprSyntax] = [
+private let mapping: [String: ExprSyntax] = [
     "String": "\"\"",
     "Int": "0",
     "Int8": "0",