BillingService Refresh Does Not Update the UI

Tapping the "Restore Purchases" button correctly gets the new status but it doesn't seem to update the UI, my fix was to add a call on `LoadProductsAsync` in `ProductsViewModel.RestorePurchasesAsync` so it now reads

```
private async Task RestorePurchasesAsync()
{
try
{
IsLoading = true;

var success = await _billingService.RestorePurchasesAsync();

if (success)
{
await (Application.Current?.Windows[0].Page?.DisplayAlertAsync("Success", "Purchases restored successfully!", "OK") ?? Task.CompletedTask);
await LoadProductsAsync(); // refresh product states
_logger.LogInformation("Purchases restored successfully");
}
else
...
```

Note that an Android you may have to refresh fairly quickly if you want to see a change after making a purchase because unacknowledged purchases by license testers are revoked after 3-5 minutes (normally it takes 3 days for an unacknowledged purchase to be revoked).