Fix #7710: isSpam data model update for WalletUserAsset

[nuo-xu]

Summary of Changes

isSpam is a new property from TokenInfo from 1.58.x. We will need to update our WalletUserAsset to have the same attribute with default value false and it will be used for the new NFT Spam Management issue #8006

This pull request fixes #7710

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()
• New or updated UI has been tested across:
  • Light & dark mode
  • Different size classes (iPhone, landscape, iPad)
  • Different dynamic type sizes

Test Plan:

1. Install a older version of Brave
2. Set up wallet and edit some visible assets
3. Upgrade to 1.58
4. Portfolio/NFT should display the same tokens.
5. Edit visible assets should still behave the same.
   No crash should occur.

Screenshots:

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue and pull request is assigned to a milestone (should happen at merge time).