Mark DeveloperDiskImageService as iOS 17.4+ to fix availability error

session.download(from:) requires iOS 15+, and this project's own
deployment target is 17.4, but consumers that vendor these sources
directly (rather than as a compiled framework) inherit their own,
potentially lower, deployment target for availability checking.

Author: CelloSerenity

Sources/DeveloperDiskImageService.swift

@@ -29,6 +29,7 @@ public struct DDIPaths: Sendable {
     }
 }
 
+@available(iOS 17.4, *)
 public actor DeveloperDiskImageService {
 
     public static let shared = DeveloperDiskImageService()

Sources/StikJIT.swift

@@ -46,6 +46,7 @@ public enum StikJIT {
     }
 
     /// Downloads the personalized Developer Disk Image files if they aren't already present at `paths`.
+    @available(iOS 17.4, *)
     public static func downloadDDIIfNeeded(to paths: DDIPaths,
                                            progress: @escaping (Double, String) -> Void = { _, _ in }) async throws {
         try await DeveloperDiskImageService.shared.downloadIfNeeded(to: paths, progress: progress)