Kebechet.Maui.RevenueCat.InAppBilling 9.0.0

• net9.0

  • Kebechet.Extensions.IsNullOrEmpty (>= 1.0.1)
  • Kebechet.Types.Result (>= 1.0.0 && < 2.0.0)
  • Microsoft.Maui.Controls (>= 9.0.0)

• net9.0-android35.0

  • Kebechet.Extensions.IsNullOrEmpty (>= 1.0.1)
  • Kebechet.Maui.RevenueCat.Android (>= 10.16.1)
  • Kebechet.Types.Result (>= 1.0.0 && < 2.0.0)
  • Microsoft.Maui.Controls (>= 9.0.0)

• net9.0-ios18.0

  • Kebechet.Extensions.IsNullOrEmpty (>= 1.0.1)
  • Kebechet.Maui.RevenueCat.iOS (>= 5.83.1)
  • Kebechet.Types.Result (>= 1.0.0 && < 2.0.0)
  • Microsoft.Maui.Controls (>= 9.0.0)

• net9.0-maccatalyst18.0

  • Kebechet.Extensions.IsNullOrEmpty (>= 1.0.1)
  • Kebechet.Maui.RevenueCat.iOS (>= 5.83.1)
  • Kebechet.Types.Result (>= 1.0.0 && < 2.0.0)
  • Microsoft.Maui.Controls (>= 9.0.0)

• net9.0-windows10.0.19041

  • Kebechet.Extensions.IsNullOrEmpty (>= 1.0.1)
  • Kebechet.Types.Result (>= 1.0.0 && < 2.0.0)
  • Microsoft.Maui.Controls (>= 9.0.0)

BREAKING
- Every asynchronous `IRevenueCatBilling` member now returns a result DTO instead of a bare value. Previously a network blip, a cancellation and a backend rejection were indistinguishable from a legitimately empty result - the RevenueCat error only ever reached the log. Read `.Value` on success; branch on `.Error`; log `.ErrorException`.
 - `CanMakePaymentsResultDto`, `IntroEligibilityResultDto`, `OfferingsResultDto`, `ProductIdentifiersResultDto`, `PurchaseDateResultDto`, `ManagementUrlResultDto`, `StorefrontResultDto`, `CustomerInfoResultDto` and `PurchaseResultDto`. Each is a thin named subclass of `DataResult<TValue, PurchaseErrorStatus>` from the `Kebechet.Types.Result` package, so signatures stay readable and every result shares one contract.
 - `PurchaseProduct()` keeps returning `PurchaseResultDto`, now a `DataResult<CustomerInfoDto, PurchaseErrorStatus>` subclass: `ErrorStatus` becomes `Error`, `ErrorMessage` becomes `ErrorException`, `CustomerInfo` becomes `Value`, and `Transaction` stays. It is a sibling of `CustomerInfoResultDto`, not a subclass of it.
- `PurchaseResultDto` is a `class`, not a `sealed record`. Value equality, `with` expressions and the record `ToString()` are gone, so `resultA == resultB` is now reference equality rather than a compile error or a value comparison. The other result DTOs are classes for the same reason - they derive from the `Kebechet.Types.Result` base types.
- `CustomerInfoDto.ManagementURL` is renamed to `CustomerInfoDto.ManagementUrl`, matching .NET acronym casing.
- New public dependency on `Kebechet.Types.Result` (1.0.0). It cannot be hidden behind `PrivateAssets` because the types appear in the public signatures.

ADDED
- `PurchaseErrorStatus` is now reported by every fallible member, so the documented failure modes can be handled exhaustively with a `switch`.
- `GetPurchaseDateForProductIdentifier()` and `GetManagementSubscriptionUrl()` distinguish "not purchased" / "no store-managed subscription" (success with a null `Value`) from a failure (`Error` set).

FIXED
- Android `GetManagementSubscriptionUrl()` returned `null` both when the user had no store subscription and when the call failed; iOS returned `string.Empty` for the former. The two cases are now distinguishable, and the platforms agree.
- `PurchaseProduct()` returned a result that was neither `IsSuccess` nor `IsError` when the transaction did not reach the purchased state. That state now reports an error while still carrying the `Transaction`: `PaymentPendingError` when the store says the payment is still settling (iOS `Deferred`, Android `PENDING`), and `UnknownError` for every other non-purchased state, which is an anomaly rather than something the user can wait out.
- `PurchaseProduct()` logged nothing at all when the native error code mapped to a cancellation - it skipped the error log without logging anything else. Every member now logs cancellation at debug and other failures at error, through one shared classifier.
- Removed the `_cachedManagementUrl` field. It was read on both platforms but never assigned, so its early-return guard could never fire. Caching it would have been wrong regardless: the URL is per-customer, so a process-lifetime cache would survive `Login`/`Logout`.
- The Windows and PlatformsStandard stubs no longer report `IsSuccess == false` together with `IsError == false` for `PurchaseProduct()`, a state that satisfied neither branch of the documented pattern. Every stub member now reports an empty success, and `GetStorefrontCountryCode()` keeps the documented `string.Empty` sentinel rather than `null`.

NOTE
- Exceptions are still thrown for developer mistakes, such as calling a member before `Initialize()`, and `CheckTrialOrIntroDiscountEligibility()` still throws `NotImplementedException` on Android.