Add Login functor

Sources/ElixxirDAppsSDK/Login.swift

+import Bindings
+import XCTestDynamicOverlay
+
+public struct Login {
+  public var run: (Int, Data, Data) throws -> E2E
+
+  public func callAsFunction(
+    cmixId: Int,
+    identity: Data,
+    e2eParamsJSON: Data
+  ) throws -> E2E {
+    try run(cmixId, identity, e2eParamsJSON)
+  }
+}
+
+extension Login {
+  public static let live = Login { cmixId, identity, e2eParamsJSON in
+    var error: NSError?
+    let bindingsE2E = BindingsLogin(
+      cmixId,
+      nil, // TODO: pass callbacks
+      identity,
+      e2eParamsJSON,
+      &error
+    )
+    if let error = error {
+      throw error
+    }
+    guard let bindingsE2E = bindingsE2E else {
+      fatalError("BindingsLogin returned `nil` without providing error")
+    }
+    return .live(bindingsE2E)
+  }
+}
+
+extension Login {
+  public static let unimplemented = Login(
+    run: XCTUnimplemented("\(Self.self)")
+  )
+}