2.1.0

Added

• A SubscriptionRevenueCatUI product, the only one that links RevenueCatUI. It carries
  RevenueCatPaywallView, which shows a paywall designed with RevenueCat Paywalls for an
  offering (the current one for nil), and PaywallContainer, which shows either that or the
  app's own paywall from one place. After a purchase or a restore the RevenueCat paywall asks the
  SubscriptionUseCase whether the customer is entitled, rather than reading the CustomerInfo
  RevenueCatUI hands back, so the configured entitlement decides and the EntitlementCache is
  refreshed; a restore that finds nothing does not count as entitled.
• PaywallMode in SubscriptionUI: .custom, .revenueCat(offering:) and
  .automatic(offering:), with .revenueCat and .automatic as shorthands for the current
  offering. A struct rather than an enum, because an enum case with an associated value and a
  static property of the same name make PaywallMode.automatic ambiguous. PaywallMode.choice(for:) is the pure rule that turns the mode and a
  PaywallOfferingLookup into a PaywallChoice; everything that stops a RevenueCat paywall from
  being shown falls back to the app's own. Held in SubscriptionUI so that an app can keep the
  setting without linking RevenueCatUI.
• PaywallHandlers: the onEntitled / onError / onDismiss that PaywallContainer passes
  to the closure building the app's own paywall, so both paywalls report in the same three
  callbacks.

Changed

• The minimum RevenueCat SDK is now 5.19.0, the first with Offering.hasPaywall.