Improve mechanism of IAP verification with the server right after purchase

It was observed that sending the receipt to the server right after
performing the StoreKit purchase caused issues due to the receipt not
being completely ready when it got sent, causing rejections by the
server.

This commit, in conjuction with backend changes, implements purchase
verification through transaction IDs directly.

Testing
--------

PASS

Device: iPhone 13 Mini (physical device)
iOS: 17.3.1
Damus: This commit
damus-api: `a878da5598a9344a4d351f9a9da16712ce0615b7`
Setup:
- Local server Setup
- Local testing mode on Damus developer settings
- Clean Sandbox account (Create new sandbox account if clearing purchase history does not work)
- Fresh DB
- App is closed before starting.
- Run app on release target
- MOCK_VERIFY=false on server, with all IAP environment correctly setup
Steps:
1. Make Purple IAP purchase. Make sure that:
    - Server logs indicate `/apple-iap/transaction-id` is being hit and returning HTTP 200. PASS
    - No errors appear on the iOS side. After purchase the welcome sheet should appear, and then the account info. PASS

Part of: https://github.com/damus-io/damus/issues/2036
Changelog-Fixed: Fix in-app purchase issue that would trigger an error on purchase before confirming the account information.

Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Signed-off-by: William Casarin <jb55@jb55.com>

damus/Models/Purple/DamusPurple.swift

@@ -120,8 +120,10 @@ class DamusPurple: StoreObserverDelegate {
                 // Record the purchase with the storekit manager, to make sure we have the update on the UIs as soon as possible.
                 // During testing I found that the purchase initiated via `purchase` was not emitted via the listener `StoreKit.Transaction.updates` until the app was restarted.
                 self.storekit_manager.record_purchased_product(StoreKitManager.PurchasedProduct(tx: tx, product: product))
-                // Send the receipt to the server
-                try await self.send_receipt()
+                await tx.finish()
+                // Send the transaction id to the server
+                try await self.send_transaction_id(transaction_id: tx.originalID)
+
             default:
                 // Any time we get a non-verified result, it means that the purchase was not successful, and thus we should throw an error.
                 throw PurpleError.iap_purchase_error(result: result)
@@ -197,6 +199,32 @@ class DamusPurple: StoreObserverDelegate {
         }
     }
 
+    func send_transaction_id(transaction_id: UInt64) async throws {
+        let account_uuid = try await self.get_maybe_cached_uuid_for_account()
+        let json_text: [String: Any] = ["transaction_id": transaction_id, "account_uuid": account_uuid.uuidString]
+        let json_data = try JSONSerialization.data(withJSONObject: json_text)
+
+        let url = environment.api_base_url().appendingPathComponent("accounts/\(keypair.pubkey.hex())/apple-iap/transaction-id")
+
+        let (data, response) = try await make_nip98_authenticated_request(
+            method: .post,
+            url: url,
+            payload: json_data,
+            payload_type: .json,
+            auth_keypair: self.keypair
+        )
+
+        if let httpResponse = response as? HTTPURLResponse {
+            switch httpResponse.statusCode {
+                case 200:
+                    Log.info("Sent transaction ID to Damus Purple server and activated successfully", for: .damus_purple)
+                default:
+                    Log.error("Error in sending or verifying transaction ID with Damus Purple server. HTTP status code: %d; Response: %s", for: .damus_purple, httpResponse.statusCode, String(data: data, encoding: .utf8) ?? "Unknown")
+                    throw DamusPurple.PurpleError.iap_receipt_verification_error(status: httpResponse.statusCode, response: data)
+            }
+        }
+    }
+
     func translate(text: String, source source_language: String, target target_language: String) async throws -> String {
         var url = environment.api_base_url()
         url.append(path: "/translate")