Add SingleUseCallback

Sources/ElixxirDAppsSDK/Callbacks/SingleUseCallback.swift

+import Bindings
+import XCTestDynamicOverlay
+
+public struct SingleUseCallback {
+  public init(handle: @escaping (Result<SingleUseCallbackReport, NSError>) -> Void) {
+    self.handle = handle
+  }
+
+  public var handle: (Result<SingleUseCallbackReport, NSError>) -> Void
+}
+
+extension SingleUseCallback {
+  public static let unimplemented = SingleUseCallback(
+    handle: XCTUnimplemented("\(Self.self)")
+  )
+}
+
+extension SingleUseCallback {
+  func makeBindingsSingleUseCallback() -> BindingsSingleUseCallbackProtocol {
+    class CallbackObject: NSObject, BindingsSingleUseCallbackProtocol {
+      init(_ callback: SingleUseCallback) {
+        self.callback = callback
+      }
+
+      let callback: SingleUseCallback
+
+      func callback(_ callbackReport: Data?, err: Error?) {
+        if let error = err {
+          callback.handle(.failure(error as NSError))
+        } else if let callbackReport = callbackReport {
+          do {
+            callback.handle(.success(try SingleUseCallbackReport.decode(callbackReport)))
+          } catch {
+            callback.handle(.failure(error as NSError))
+          }
+        } else {
+          fatalError("BindingsSingleUseCallback received `nil` callbackReport and `nil` error")
+        }
+      }
+    }
+
+    return CallbackObject(self)
+  }
+}