chore: change default network avatar style (#28976)

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## **Description**
This PR changes the default position of the network avatar to the
bottomRight of the token. It also changes the default shape from a
circle to a rounded square

Figma:
https://www.figma.com/design/IuOIRmU3wI0IdJIfol0ESu/Cross-Chain-Swaps?node-id=7-24563&node-type=canvas&m=dev

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[![Open in GitHub
Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/28976?quickstart=1)

## **Related issues**

Fixes: N/A

## **Manual testing steps**

1. Visually inspect AvatarNetwork instances (token list, network picker,
activity, etc

## **Screenshots/Recordings**

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

### **Before**
![Screenshot 2024-12-09 at 11 20
35 AM](https://github.com/user-attachments/assets/46711271-ef5a-4d1d-a9b6-fea93cd3bed4)
![Screenshot 2024-12-09 at 11 20
40 AM](https://github.com/user-attachments/assets/28fd5c27-d91a-49b1-ba60-5e240f1a768e)



### **After**
![Screenshot 2024-12-09 at 11 18
59 AM](https://github.com/user-attachments/assets/67ed09a8-befb-49a0-ad6b-5c4d65ad428c)
![Screenshot 2024-12-09 at 11 18
45 AM](https://github.com/user-attachments/assets/6ae812aa-988b-48e0-befb-702c7fc664ec)


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

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Extension Coding
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- [X] I've completed the PR template to the best of my ability
- [X] I’ve included tests if applicable
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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.