Statistics and APKG import fail with Protobuf errors after reviewer creates large cookies

### Checked for duplicates?

- [x] This issue is not a duplicate

### Does it also happen in the desktop version?

- [ ] This bug does not occur in the latest version of Anki Desktop

### What are the steps to reproduce this bug?

I can reproduce this on a clean Android 16 / API 36 emulator with 4 KB pages, AnkiDroid 2.24.0, and Android System WebView 147.0.7727.137. The attached ZIP contains a one-card APKG with no media, its complete front template, and the script used to build it.

1. Import `ankidroid-loopback-cookie-reproducer.apkg`.
2. Open its only card once. It creates 24 local test cookies and reports 60,718 characters. It makes no network requests.
3. Open Statistics. It fails with `Error: 500: ProtoError { info: "failed to decode Protobuf message: invalid wire type value: 7" }`.
4. Select the same APKG again and press Import on the import-options screen. It fails with `500: Protocol message contained an invalid tag (zero).`

The card has a Clear test cookies button. After using it, Statistics loads normally again without reinstalling AnkiDroid. The test cookies also expire after one hour.

[ankidroid-loopback-cookie-reproducer.zip](https://github.com/user-attachments/files/31556916/ankidroid-loopback-cookie-reproducer.zip)

### Expected behaviour

Statistics should load, and importing the same valid APKG again should complete without a Protobuf decoding error.

### Debug info

```text
AnkiDroid Version = 2.24.0 (ebcf8e0e34921628b9b8a496c66ffd4adbb3705f)
Backend Version = 0.1.64-anki25.09.2 (25.09.2 3890e12c9e48c028c3f12aa58cb64bd9f8895e30)
Android Version = 16 (SDK 36)
ProductFlavor = full
Device Info = Google | google | emu64a | sdk_gphone64_arm64 | sdk_gphone64_arm64 | ranchu
WebView Info = [com.google.android.webview | 772713704]: Mozilla/5.0 (Linux; Android 16; sdk_gphone64_arm64 Build/BE2A.250530.026.F3; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/147.0.7727.137 Mobile Safari/537.36
ACRA UUID = 09950e2a-bb8b-4644-be60-eb643b26802a
FSRS = 5.1.0 (Enabled: false)
Crash Reports Enabled = true
```

### (Optional) Anything else you want to share?

I built the APKG from [`AnkiDroid/src/androidTest/assets/update1.apkg`](https://github.com/ankidroid/Anki-Android/blob/ebcf8e0e34921628b9b8a496c66ffd4adbb3705f/AnkiDroid/src/androidTest/assets/update1.apkg). The included script replaces only the card template, names, description, and note fields, then re-zips `collection.anki2` and `media`. APKG SHA-256: `562905cb853b23c93dc6bcbb6cc70318a643ef448388c37d1c909b07f17cf7ae`. ZIP SHA-256: `6e30e6a83e551b06f7c20d1e5d7507ffc5c03d3859467d3f0731738967b24d6a`.

I checked the exact APKG with Anki Desktop's bundled backend 25.09.2 (`3890e12c`) in a disposable collection. It imported as one note and one card, and both the 365-day and all-history `graphs` calls completed successfully.

Related: #21412. That report focused on the reviewer JavaScript API and was closed after treating a cookie header over 8 KiB as add-on misuse. This reproducer shows the same cookie jar also breaks AnkiDroid's built-in Statistics and APKG import. This is the self-contained new report requested after #21618 was closed.

### Research

- [x] I have checked the [manual](https://docs.ankidroid.org/) and the [FAQ](https://github.com/ankidroid/Anki-Android/wiki/FAQ) and could not find a solution to my issue
- [ ] (Optional) I have confirmed the issue is not resolved in the latest alpha release ([instructions](https://docs.ankidroid.org/manual.html#betaTesting))