Add ContactFactsSetter

Sources/ElixxirDAppsSDK/ContactFactsSetter.swift

+import Bindings
+
+public struct ContactFactsSetter {
+  public var set: (Data, Data) throws -> Data
+
+  public func callAsFunction(contact: Data, facts: Data) throws -> Data {
+    try set(contact, facts)
+  }
+}
+
+extension ContactFactsSetter {
+  public static let live = ContactFactsSetter { contact, facts in
+    var error: NSError?
+    let updatedContact = BindingsSetFactsOnContact(contact, facts, &error)
+    if let error = error {
+      throw error
+    }
+    guard let updatedContact = updatedContact else {
+      fatalError("BindingsSetFactsOnContact returned `nil` without providing error")
+    }
+    return updatedContact
+  }
+}
+
+#if DEBUG
+extension ContactFactsSetter {
+  public static let failing = ContactFactsSetter { _, _ in
+    struct NotImplemented: Error {}
+    throw NotImplemented()
+  }
+}
+#endif