… reset on asset change cp-7.72.0 (#28086)

## **Description**

When switching between perps assets (e.g. from BTC to ETH), the "Pay
with" token selection could get out of sync — the pending config from
the previous asset would either not be restored or would conflict with
the newly selected asset's payment token.


## **Changelog**

CHANGELOG entry: Fixed payment token not restoring correctly when
switching between perps assets

## **Related issues**

Fixes jira issue:
https://consensyssoftware.atlassian.net/browse/TAT-2785

## **Manual testing steps**

```gherkin
Feature: Perps pay-with token persistence across asset switches

  Scenario: User switches perps asset and pending pay token is restored
    Given the user has a pending pay-with token config saved for ETH perps
    And the user is currently viewing BTC perps order view

    When the user switches to ETH perps
    Then the pay-with token row displays the previously saved payment token for ETH

  Scenario: User switches asset and controller state is reset
    Given the user is viewing BTC perps with a selected payment token

    When the user switches to ETH perps
    Then the controller's selectedPaymentToken is reset to null
    And the new asset's pending config (if any) is applied

  Scenario: User opens perps with no prior selectedPaymentToken in controller
    Given the user has a pending pay-with config but no selectedPaymentToken in the controller

    When the user opens the perps order view
    Then the pending config is applied and the correct pay token is displayed
```

## **Screenshots/Recordings**

N/A — no UI changes, logic-only fix in payment token sync.

### **Before**

N/A

### **After**

N/A

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **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]
> **Medium Risk**
> Touches perps payment-token synchronization logic and controller state
resets, which can affect what token a user trades with across asset
switches. Changes are localized and covered by new unit tests, but
regressions could impact user transaction configuration.
> 
> **Overview**
> Fixes perps “Pay with” token desynchronization when switching
`initialAsset` by **clearing `PerpsController.setSelectedPaymentToken`
on asset change** and ensuring pending token config is re-applied for
the new asset.
> 
> Adjusts pending-config sync so it can apply even when
`selectedPaymentToken` is `null`, and only re-syncs when either the
`payToken` *or* controller-selected token differs from the pending token
(avoiding unnecessary overwrites). Adds targeted tests covering
asset-change cleanup and the new sync edge cases.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
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<!-- /CURSOR_SUMMARY -->