Fix compilation issues

Sources/Mailgun/Extensions/MailgunClient+encode.swift

@@ -1,3 +1,9 @@
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
+import Foundation
+#endif
+
 extension MailgunClient {
     func encode(apiKey: String) throws -> String {
         guard let apiKeyData = "api:\(apiKey)".data(using: .utf8) else {

Sources/Mailgun/Extensions/MailgunClient+parse.swift

@@ -1,3 +1,4 @@
+import NIOFoundationCompat
 import Vapor
 
 extension MailgunClient {

Sources/Mailgun/Models/MailgunIncomingMessage.swift

@@ -1,4 +1,4 @@
-import Vapor
+public import Vapor
 
 public struct MailgunIncomingMessage: Content {
     public static var defaultContentType: HTTPMediaType { .formData }
@@ -49,7 +49,7 @@ public struct MailgunIncomingMessage: Content {
         }
     }
 
-    public init(from decoder: Decoder) throws {
+    public init(from decoder: any Decoder) throws {
         let container = try decoder.container(keyedBy: CodingKeys.self)
         recipient = try container.decode(String.self, forKey: .recipient)
         sender = try container.decode(String.self, forKey: .sender)
@@ -65,7 +65,7 @@ public struct MailgunIncomingMessage: Content {
 
         var _attachments: [File] = []
         let attachmentsContainer = try decoder.container(keyedBy: DynamicAttachmentKey.self)
-        try attachmentsContainer.allKeys.forEach { attachmentKey in
+        for attachmentKey in attachmentsContainer.allKeys {
             _attachments.append(try attachmentsContainer.decode(File.self, forKey: attachmentKey))
         }
         attachments = _attachments

Sources/Mailgun/Models/MailgunRouteSetup.swift

@@ -1,6 +1,11 @@
-import Foundation
 public import Vapor
 
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
+import Foundation
+#endif
+
 public struct MailgunRouteSetup: Content {
     public static var defaultContentType: HTTPMediaType { .urlEncodedForm }
 

Sources/Mailgun/Models/MailgunTemplate.swift

@@ -1,8 +1,8 @@
-import Vapor
+public import Vapor
 
 /// Template, see https://documentation.mailgun.com/en/latest/api-templates.html#templates
 public struct MailgunTemplate: Content {
-    public static let defaultContentType: HTTPMediaType { .formData }
+    public static var defaultContentType: HTTPMediaType { .formData }
 
     public let name: String
     public let description: String

Tests/MailgunTests/MailgunTests.swift

@@ -4,7 +4,7 @@ import SystemPackage
 import Testing
 import VaporTesting
 
-@Suite("Mailgun Tests")
+@Suite("Mailgun Tests", .serialized)
 struct MailgunTests {
     private func configure(_ app: Application) async throws {
         let config = ConfigReader(providers: [