feat: implement decode method

[gorhom]

introduce a new method to instantiate a Codable model that extends BaseCodable

usage

class Post extends BaseCodable {
  title!: string;
  isActive?: boolean;
}

Post.CodingProperties = {
  title: types.string,
  isActive: {
    type: types.optional(types.boolean),
    key: 'active',
  },
};

const post = decode(Post, {
  title: "dummy post",
  active: true
});