fix: remove duplicate POL tokens from swap select token screen (#21924)

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## **Description**

POL token is defined with zero address in our backend services but its
actual address is `0x0000000000000000000000000000000000001010`. That
creates an issue where both tokes are rendered even if they are the
same. To mitigate this issue we keep the one with zero address as it's
more consistent with similar logic.

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## **Changelog**

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CHANGELOG entry: Fixes an issue where users will see two POL tokens on
swap select token screen

## **Related issues**

Fixes: #19334

## **Manual testing steps**

```gherkin
- Ensure that users see only one POL token on Select Token screen of swaps.
- Ensure that POL token rendered in Select Token screen of swaps have correct balance.
- Ensure that users can complete a swap or bridge transaction using POL token both as source and dest.
```

## **Screenshots/Recordings**

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before and after of your change. -->

### **Before**

<!-- [screenshots/recordings] -->
<img width="429" height="878" alt="Screenshot 2025-10-30 at 11 40 04 AM"
src="https://github.com/user-attachments/assets/13d41b1a-2f52-4070-9f47-ca8c38263629"
/>


### **After**
<img width="449" height="909" alt="Screenshot 2025-10-30 at 2 18 18 PM"
src="https://github.com/user-attachments/assets/d11a437c-56dc-4733-b1cc-835cb792ce2f"
/>

<!-- [screenshots/recordings] -->

## **Pre-merge author checklist**

- [x] I’ve followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
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- [x] I've completed the PR template to the best of my ability
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## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Normalize Polygon native token addressing to dedupe POL across token
sources and ensure correct rendering/exclusion.
> 
> - **Bridge tokens**:
> - Normalize Polygon native token by mapping
`0x0000000000000000000000000000000000001010` to `zeroAddress()` in
`useTokens` `getTokenKey` for consistent deduplication across sources.
> - Respect exclusions for POL regardless of whether specified as
`zeroAddress()` or native address.
> - **Tests**:
>   - Add comprehensive tests in `hooks/useTokens.test.ts` covering:
> - Duplicate prevention between `tokensWithBalance` and `topTokens`
(both address variants).
> - Mixed-chain behavior (ETH unaffected), `allTokens` normalization,
and exclusion cases.
> - **Constants**:
>   - Introduce `POLYGON_NATIVE_TOKEN` in `constants/assets.ts`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
3cde5f8. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: GeorgeGkas

app/components/UI/Bridge/constants/assets.ts

@@ -0,0 +1,2 @@
+export const POLYGON_NATIVE_TOKEN =
+  '0x0000000000000000000000000000000000001010';