[Bug] FirebaseAuth anonymous sign-in fails after Application.Unload() on Android

### Description

Description:
After signing in anonymously and querying Firestore, calling Application.Unload() prevents subsequent sign-ins.

Expected vs Actual:
Expected: sign in successfully after unload.
Actual: user stays nul

What i've tried:
Calling Dispose() on FirebaseApp or FirebaseAuth before Application.Unload() does not allow a successful re-sign-in.

### Reproducing the issue

Sign In Anonymously → works.
Query Firestore Document → works.
Application.Unload().
ReOpen the app.
Try Sign In Anonymously again → user remains null (stuck in the Task & no error thrown)

### Firebase Unity SDK Version

Tested on 13.9.0 and 12.10.1

### Unity editor version

6000.0.59f2

### Installation Method

.unitypackage

### Problematic Firebase Component(s)

Authentication

### Other Firebase Component(s) in use

Firestore

### Additional SDKs you are using

I am using the .tgz files.

### Targeted Platform(s)

Android

### Unity editor platform

Windows

### Scripting Runtime

IL2CPP

### Release Distribution Type

Open-source from this repo

### Relevant Log Output

```shell
16:39:41.878 I [FIREBASE_DEBUG] Start() - Firebase will not sign in automatically.
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
16:39:44.958 I [FIREBASE_DEBUG] Button: Sign In
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:OnGUI()
16:39:44.958 W [FIREBASE_DEBUG] Auth is null, initializing Firebase...
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:39:44.959 I [FIREBASE_DEBUG] InitializeFirebase() called
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:InitializeFirebase()
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:39:45.020 I [FIREBASE_DEBUG] Firebase initialized. App name: __FIRAPP_DEFAULT
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:39:45.021 I [FIREBASE_DEBUG] Starting anonymous sign-in...
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:39:45.272 I [FIREBASE_DEBUG] User signed in: IyjqQUO6yLdBHz5jmyzVE42C2TK2
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:b__8_0(Task`1)
Firebase.Extensions.<>c__DisplayClass4_1`1:b__1()
Firebase.<>c__DisplayClass5_0`1:b__0()
Firebase.ExceptionAggregator:Wrap(Action)
Firebase.Dispatcher:PollJobs()
Firebase.Platform.FirebaseHandler:Update()
16:40:00.376 I [FIREBASE_DEBUG] Button: Query Firestore Document
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:OnGUI()
16:40:00.377 I [FIREBASE_DEBUG] Running Firestore test query document...
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:QueryTestFirestore()
DebugSceneController:OnGUI()
16:40:00.714 I [FIREBASE_DEBUG] Firestore query success. Document exists: True
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
<>c:b__9_0(Task`1)
Firebase.Extensions.<>c__DisplayClass4_1`1:b__1()
Firebase.<>c__DisplayClass5_0`1:b__0()
Firebase.ExceptionAggregator:Wrap(Action)
Firebase.Dispatcher:PollJobs()
Firebase.Platform.FirebaseHandler:Update()
16:40:10.243 I [FIREBASE_DEBUG] Button: Application.Unload()
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:OnGUI()
16:40:14.746 I [FIREBASE_DEBUG] Start() - Firebase will not sign in automatically.
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
16:40:20.196 I [FIREBASE_DEBUG] Button: Sign In
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:OnGUI()
16:40:20.196 W [FIREBASE_DEBUG] Auth is null, initializing Firebase...
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:40:20.197 I [FIREBASE_DEBUG] InitializeFirebase() called
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:InitializeFirebase()
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:40:20.198 I [FIREBASE_DEBUG] Firebase initialized. App name: __FIRAPP_DEFAULT
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:40:20.199 I [FIREBASE_DEBUG] Starting anonymous sign-in...
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:SignInAnonymously()
DebugSceneController:OnGUI()
16:40:38.624 I [FIREBASE_DEBUG] Button: Query Firestore Document
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:OnGUI()
16:40:38.624 W [FIREBASE_DEBUG] Cannot query Firestore: user not signed in
UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
DebugSceneController:OnGUI()
```

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Expand Podfile.lock snippet

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👀 Replace this line with the contents of your Podfile.lock!

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