This change introduces the UnityBannerAdPreloader class, which wraps the GMA SDK's BannerAdPreloader. It provides methods to start preloading banner ads, check ad availability, poll preloaded ads, and manage preload configurations. Callbacks from the GMA SDK are executed on a separate thread to avoid blocking the Unity main thread. Unit tests are included to verify the functionality of the UnityBannerAdPreloader.#4159