Play Billing Library 8 support in Purchases SDK v9.0.0

Google Play Billing Library 8 introduces several enhancements, including multiple purchase options for one-time products, support for non-expiring subscriptions, and new Kotlin extensions, which aim to simplify product management and error handling for developers. Notable updates include the renaming of "in-app items" to "one-time products," enhancements to queryProductDetailsAsync(), and the automatic service reconnection feature in BillingClient. The update also involves the removal of several deprecated APIs and introduces sub-response codes for specific error cases. Developers transitioning to RevenueCat SDK v9.0.0 can expect a smooth migration process, with minimal changes required if they are already using the recommended versions of Kotlin, Flutter, or Dart. The update does not affect RevenueCat iOS SDK users and focuses on streamlining the integration process for Android, Kotlin Multiplatform, Flutter, and React Native platforms, allowing developers to concentrate on app development while RevenueCat handles the billing complexities.