Add missing imports to fix Swift 6.1+

Author: czechboy0

Sources/_OpenAPIGeneratorCore/Extensions/SwiftStandardLibrary.swift

@@ -11,6 +11,8 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 //===----------------------------------------------------------------------===//
+import Foundation
+
 extension Int {
     /// Returns the digits for the number using the specified radix.
     /// - Parameter radix: The radix used to format the integer.

Sources/_OpenAPIGeneratorCore/Translator/CommonTypes/StructBlueprint.swift

@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 import OpenAPIKit
+import Foundation
 
 /// A structure that contains the information about an OpenAPI object that is
 /// required to generate a matching Swift structure.

Sources/_OpenAPIGeneratorCore/Translator/Content/ContentInspector.swift

@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 import OpenAPIKit
+import Foundation
 
 /// Utilities for asking questions about OpenAPI.Content
 extension FileTranslator {

Sources/_OpenAPIGeneratorCore/Translator/TypesTranslator/translateServersVariables.swift

@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 import OpenAPIKit
+import Foundation
 
 /// Represents a server variable and the function of generation that should be applied.
 protocol ServerVariableGenerator {