Add ContactFact codable model

Sources/ElixxirDAppsSDK/ContactFact.swift

+public struct ContactFact: Equatable {
+  public init(
+    fact: String,
+    type: Int
+  ) {
+    self.fact = fact
+    self.type = type
+  }
+
+  public var fact: String
+  public var type: Int
+}
+
+extension ContactFact: Codable {
+  enum CodingKeys: String, CodingKey {
+    case fact = "Fact"
+    case type = "Type"
+  }
+}

Tests/ElixxirDAppsSDKTests/ContactFactTests.swift

+import CustomDump
+import XCTest
+@testable import ElixxirDAppsSDK
+
+final class ContactFactTests: XCTestCase {
+  func testCoding() throws {
+    let jsonString = """
+    {
+      "Fact": "Zezima",
+      "Type": 0
+    }
+    """
+    let jsonData = jsonString.data(using: .utf8)!
+    let decoder = JSONDecoder()
+    decoder.dataDecodingStrategy = .base64
+    let fact = try decoder.decode(ContactFact.self, from: jsonData)
+
+    XCTAssertNoDifference(fact, ContactFact(
+      fact: "Zezima",
+      type: 0
+    ))
+
+    let encoder = JSONEncoder()
+    encoder.dataEncodingStrategy = .base64
+    let encodedFact = try encoder.encode(fact)
+    let decodedFact = try decoder.decode(ContactFact.self, from: encodedFact)
+
+    XCTAssertNoDifference(decodedFact, fact)
+  }
+}