[in_app_purchase] Fixes StoreKit 2 date format does not match in_app_purchase_platform_interface

## Description

- As per `PurchaseDetails.transactionDate` api documentation, date should be `Milliseconds since epoch` but the migration to StoreKit2 probably mistakenly changed the date format to "yyyy-MM-dd HH:mm:ss". The issue originated in StoreKit2Translators.swift `extension Transaction convertToPigeon` which was using a magic hardcoded formatter dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
- Fixes both `SK2Transaction.purchaseDate` and `SK2Transaction.expirationDate` and ultimately `PurchaseDetails.transactionDate`

## Tests

Unfortunately it is not testable because the StoreKit 2 Transaction type has no visible initializers, probably thats why there are no tests for StoreKit2Translators.swift `extension Transaction convertToPigeon`

## Related Issues

Fixes flutter/flutter#175072

Author: absar

packages/in_app_purchase/in_app_purchase_storekit/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.4.9
+
+* Fixes StoreKit 2 date format does not match in_app_purchase_platform_interface PurchaseDetails.transactionDate format. 
+  Fixes both `SK2Transaction.purchaseDate` and `SK2Transaction.expirationDate`.
+
 ## 0.4.8+1
 
 * Fixes StoreKit 2 purchase flow to send cancelled/pending/unverified results to `purchaseStream`.

packages/in_app_purchase/in_app_purchase_storekit/darwin/in_app_purchase_storekit/Sources/in_app_purchase_storekit/StoreKit2/StoreKit2Translators.swift

@@ -194,16 +194,12 @@ extension Product.PurchaseResult {
 extension Transaction {
   func convertToPigeon(receipt: String?, status: SK2PurchaseStatusMessage) -> SK2TransactionMessage
   {
-
-    let dateFormatter = DateFormatter()
-    dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
-
     return SK2TransactionMessage(
       id: Int64(id),
       originalId: Int64(originalID),
       productId: productID,
-      purchaseDate: dateFormatter.string(from: purchaseDate),
-      expirationDate: expirationDate.map { dateFormatter.string(from: $0) },
+      purchaseDate: String(Int64(purchaseDate.timeIntervalSince1970 * 1000)),
+      expirationDate: expirationDate.map { String(Int64($0.timeIntervalSince1970 * 1000)) },
       purchasedQuantity: Int64(purchasedQuantity),
       appAccountToken: appAccountToken?.uuidString,
       receiptData: receipt,

packages/in_app_purchase/in_app_purchase_storekit/pubspec.yaml

@@ -2,7 +2,7 @@ name: in_app_purchase_storekit
 description: An implementation for the iOS and macOS platforms of the Flutter `in_app_purchase` plugin. This uses the StoreKit Framework.
 repository: https://github.com/flutter/packages/tree/main/packages/in_app_purchase/in_app_purchase_storekit
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+in_app_purchase%22
-version: 0.4.8+1
+version: 0.4.9
 
 environment:
   sdk: ^3.9.0