[Bug]: importTransactions API won't check for duplicates in same import

### Verified issue does not already exist?

- [x] I have searched and found no existing issue

### What happened?

I'm currently writing an CSV importer and noticed a minor bug in the importTransactions API function.

I created a hash from an row in the CSV file to detect duplicates and to create the `imported_id`.

If a duplicated transaction with the same `imported_id` is imported in the same importTransactions API call, it will still be imported. If the calls are after each other, it works just fine how it should.

### How can we reproduce the issue?

POC Code

```js
import * as api from "@actual-app/api";
import fs from "fs";
import dotenv from "dotenv";

dotenv.config();

const SERVER_URL = process.env.SERVER_URL;
const ACTUAL_PASSWORD = process.env.ACTUAL_PASSWORD;
const SYNC_ID = process.env.SYNC_ID;
const E2E_PASSWORD = process.env.E2E_PASSWORD;

async function testImportTransactions() {
const cacheDir = './local-budgets-cache';
if (!fs.existsSync(cacheDir)) {
fs.mkdirSync(cacheDir, { recursive: true });
console.log(`✔ Created missing directory: ${cacheDir}`);
}

await api.init({
dataDir: cacheDir,
serverURL: SERVER_URL,
password: ACTUAL_PASSWORD,
});

await api.downloadBudget(SYNC_ID, E2E_PASSWORD ? { password: E2E_PASSWORD } : undefined);

// Create a new test account
const accountId = await api.createAccount({ name: "Testaccount" });

// Import transactions at the same time with the same imported_id
let result = await api.importTransactions(accountId, [
{
date: "2024-02-01",
amount: 10000, // 100.00
notes: "#1",
imported_id: "duplicate-id",
},
{
date: "2024-02-02",
amount: 20000, // 200.00
notes: "#2",
imported_id: "duplicate-id",
}
]);

// Import transactions separately with the same imported_id
result = await api.importTransactions(accountId, [
{
date: "2024-02-03",
amount: 10000, // 100.00
notes: "#3",
imported_id: "duplicate-id-2",
}
]);
result = await api.importTransactions(accountId, [
{
date: "2024-02-04",
amount: 20000, // 200.00
notes: "#4",
imported_id: "duplicate-id-2",
}
]);

await api.shutdown();
}

// Run the test
testImportTransactions().catch(console.error);
```

Result: `#1`, `#2` and `#3` are created.
Expected behaviour: `#1` and `#3` are created.

### Where are you hosting Actual?

Docker

### What browsers are you seeing the problem on?

_No response_

### Operating System

None