Refactor GPlay billing error handling and translations

This commit introduces localized error messages for Google Play billing issues and refactors the error handling in `UpgradeRepoGplay`.

- `BillingException` and `BillingResultException` now implement `HasLocalizedError` to provide user-friendly error messages.
- New string translations for billing error labels and descriptions have been added for various languages.
- `UpgradeRepoGplay` now includes an `error` field in its `Info` state to propagate billing errors.
- The `upgradeInfo` flow in `UpgradeRepoGplay` has been updated with a `retryWhen` operator to handle errors more gracefully. If an error occurs but the pro state was recent, it emits a grace period state. Otherwise, it emits the error.
- `OverviewFragmentVM` now observes `upgradeState` and posts any non-pro errors to `errorEvents` for display.

app/src/foss/java/eu/darken/capod/common/upgrade/core/UpgradeControlFoss.kt

@@ -64,6 +64,7 @@ class UpgradeControlFoss @Inject constructor(
         override val isPro: Boolean = false,
         override val upgradedAt: Instant? = null,
         val upgradeReason: FossUpgrade.Reason? = null,
+        override val error: Throwable? = null,
     ) : UpgradeRepo.Info {
         override val type: UpgradeRepo.Type = UpgradeRepo.Type.FOSS
     }