import HMAC1 users with different hash algorithm keys one after another not setting correct passwords

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### [REQUIRED] Step 2: Describe your environment

* Operating System version: windows 10
* Firebase SDK version: 12.1.1
* Firebase Product: admin
* Node.js version: 20.11.0
* NPM version: 10.2.4

### [REQUIRED] Step 3: Describe the problem
When using the importUsers function, it is not correctly importing users where each one has a different hash key.

I am importing users where each user's password was created using HMAC sha1 but each user had its own key. I was trying to import 1 user per function call but when I import say 100 users one at a time, the majority of them import incorrectly(code below should make this easy to understand) . If I rerun a subset of around 10 users using the exact same information passed in they then will login correctly.

Is there some internal limitation or batching happening? I am importing users one at a time and respecting the API quotas and they are successful imports. This has been very confusing to understand the correct way to handle this scenario is and it feels difficult to understand a pattern.

Given they all import with no issues but only some actually log in correctly and when I rerun then more will work, tells me I am not passing in bad data but something about how they process is different each time.

#### Steps to reproduce:

What happened? How can we make the problem occur?
This could be a description, log/console output, etc.

#### Relevant Code:
The code below will generate 100 users and import them one at a time and then when I attempt to log in, only the last 10 ish will even work, all others get incorrect password errors.

```
const crypto = require('crypto');
const admin = require('firebase-admin');

var serviceAccount = require(".\\key.json");
admin.initializeApp({
credential: admin.credential.cert(serviceAccount),
});

const randomString = (length) => {
return Math.random().toString(36).slice(2, length + 2)
}

const users = [];
for(let i = 0; i <= 100; i++) {
const text = 'password'
const key = randomString(12);
const passwordHash = crypto.createHmac('sha1', key)
.update(text)
.digest('hex')

users.push({
plainPassword: text,
passwordHash,
key,
email_address: `${i}@gmail.com`,
id: i.toString()
})
}

async function start() {
for (const user of users) {
const result = await admin.auth().importUsers([
{
uid: user.id,
email: user.email_address,
passwordHash: Buffer.from(user.passwordHash, 'hex'),
emailVerified: true
}
], {
hash: {
algorithm: "HMAC_SHA1",
key: Buffer.from(user.key)
}
})

console.log(result.errors[0]);
}
}

start();
```

Start at the admin.auth().importUsers entry point and trace how the hash option and per-user HMAC_SHA1 key are handled across sequential imports. Reproduce the supplied script, then verify that users imported with different keys all authenticate with their supplied passwords and that import results remain successful.

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