Add PasswordGenerator

Sources/ElixxirDAppsSDK/Errors.swift

 public struct BindingsDownloadAndVerifySignedNdfWithUrlUnknownError: Error, Equatable {
   public init() {}
 }
+
+public struct BindingsGenerateSecretUnknownError: Error, Equatable {
+  public init() {}
+}

Sources/ElixxirDAppsSDK/PasswordGenerator.swift

+import Bindings
+
+public struct PasswordGenerator {
+  public var run: () throws -> Data
+
+  public func callAsFunction() throws -> Data {
+    try run()
+  }
+}
+
+extension PasswordGenerator {
+  public static let live = PasswordGenerator {
+    guard let secret = BindingsGenerateSecret(32) else {
+      throw BindingsGenerateSecretUnknownError()
+    }
+    return secret
+  }
+}
+
+#if DEBUG
+extension PasswordGenerator {
+  public static let failing = PasswordGenerator {
+    struct NotImplemented: Error {}
+    throw NotImplemented()
+  }
+}
+#endif