Add ChannelDef model

Sources/ElixxirDAppsSDK/Models/ChannelDef.swift

+import Foundation
+
+public struct ChannelDef: Equatable {
+  public init(
+    name: String,
+    description: String,
+    salt: Data,
+    pubKey: Data
+  ) {
+    self.name = name
+    self.description = description
+    self.salt = salt
+    self.pubKey = pubKey
+  }
+
+  public var name: String
+  public var description: String
+  public var salt: Data
+  public var pubKey: Data
+}
+
+extension ChannelDef: Codable {
+  enum CodingKeys: String, CodingKey {
+    case name = "Name"
+    case description = "Description"
+    case salt = "Salt"
+    case pubKey = "PubKey"
+  }
+
+  public static func decode(_ data: Data) throws -> Self {
+    try JSONDecoder().decode(Self.self, from: data)
+  }
+
+  public func encode() throws -> Data {
+    try JSONEncoder().encode(self)
+  }
+}

Tests/ElixxirDAppsSDKTests/Models/ChannelDefTests.swift

+import CustomDump
+import XCTest
+@testable import ElixxirDAppsSDK
+
+final class ChannelDefTests: XCTestCase {
+  func testCoding() throws {
+    let name = "My broadcast channel"
+    let description = "A broadcast channel for me to test things"
+    let saltB64 = "gpUqW7N22sffMXsvPLE7BA=="
+    let pubKeyB64 = "LS0tLS1CRUdJTiBSU0EgUFVCTElDIEtFWS0tLS0tCk1DZ0NJUUN2YkZVckJKRFpqT3Y0Y0MvUHZZdXNvQkFtUTFkb3Znb044aHRuUjA2T3F3SURBUUFCCi0tLS0tRU5EIFJTQSBQVUJMSUMgS0VZLS0tLS0="
+    let jsonString = """
+    {
+      "Name": "\(name)",
+      "Description": "\(description)",
+      "Salt": "\(saltB64)",
+      "PubKey": "\(pubKeyB64)"
+    }
+    """
+    let jsonData = jsonString.data(using: .utf8)!
+    let model = try ChannelDef.decode(jsonData)
+
+    XCTAssertNoDifference(model, ChannelDef(
+      name: name,
+      description: description,
+      salt: Data(base64Encoded: saltB64)!,
+      pubKey: Data(base64Encoded: pubKeyB64)!
+    ))
+
+    let encodedModel = try model.encode()
+    let decodedModel = try ChannelDef.decode(encodedModel)
+
+    XCTAssertNoDifference(decodedModel, model)
+  }
+}