Add InitFileTransfer functor

Sources/ElixxirDAppsSDK/Functors/InitFileTransfer.swift

+import Bindings
+import XCTestDynamicOverlay
+
+public struct InitFileTransfer {
+  public var run: (Int, Data, Data, ReceiveFileCallback) throws -> FileTransfer
+
+  public func callAsFunction(
+    e2eId: Int,
+    e2eFileTransferParamsJSON: Data,
+    fileTransferParamsJSON: Data,
+    callback: ReceiveFileCallback
+  ) throws -> FileTransfer {
+    try run(e2eId, e2eFileTransferParamsJSON, fileTransferParamsJSON, callback)
+  }
+}
+
+extension InitFileTransfer {
+  public static let live = InitFileTransfer {
+    e2eId, e2eFileTransferParamsJSON, fileTransferParamsJSON, callback in
+
+    var error: NSError?
+    let bindingsFileTransfer = BindingsInitFileTransfer(
+      e2eId,
+      callback.makeBindingsReceiveFileCallback(),
+      e2eFileTransferParamsJSON,
+      fileTransferParamsJSON,
+      &error
+    )
+    if let error = error {
+      throw error
+    }
+    guard let bindingsFileTransfer = bindingsFileTransfer else {
+      fatalError("BindingsInitFileTransfer returned `nil` without providing error")
+    }
+    return .live(bindingsFileTransfer)
+  }
+}
+
+extension InitFileTransfer {
+  public static let unimplemented = InitFileTransfer(
+    run: XCTUnimplemented("\(Self.self)")
+  )
+}