chore: Improve account list performance (#14910)

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## **Description**
This is a minor PR that aims to improve the rendering performance of the
AccountsList component with some basic tricks. This PR has no functional
differences with what is already in main.

1. extract inline functions into their own variables so that they can be
memoized
2. remove the need to iterate over all the accounts in the
AccountsController. Instead we simple lookup the account via address.
3. memoize the component 
4. memoize the icon selector with a shallow equal.

None of these will make massive improvements but they are best practices
and could give us small benefits. It also makes the component easier to
reason about.

## **Related issues**

Fixes:

## **Manual testing steps**

1. create/import a wallet
2. click on the selected account at the top of the screen
3. once the account list opens, all of your accounts with the correct
names and balances should render
4. selecting a new account should change your selected account 
5. editing an account name should properly change the name in the list
and the home page.

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**


### **After**


https://github.com/user-attachments/assets/88724a2f-1c5f-4a2b-944f-ce6dfd2a31f0



## **Pre-merge author checklist**

- [ ] 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).
- [ ] I've completed the PR template to the best of my ability
- [ ] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] 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.

Author: owencraston