feat: support adding non-evm tokens

[juanmigdr]

Explanation

The feature to hide tokens is now available for NON-EVM assets but there is no way to bring the assets back. This task involves implementing a token import feature for non-EVM assets. This is crucial for improving user experience by allowing users to import. The implementation should be prioritized to align with upcoming Solana campaigns.

References

https://consensyssoftware.atlassian.net/browse/ASSETS-1425

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

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Note

Adds MultichainAssetsController:addAsset to manually add non‑EVM assets (with metadata refresh, dedupe, unignore, and event emission) and updates MultichainBalancesController to set zero balance for newly added assets missing snap balances.

• Multichain Assets:
  • New Action: Add addAsset to MultichainAssetsController (registers action handler, updates accountsAssets, refreshes metadata, removes from allIgnoredAssets, dedupes, and publishes MultichainAssetsController:accountAssetListUpdated).
  • Types: Extend MultichainAssetsControllerActions with MultichainAssetsControllerAddAssetAction.
  • Tests: Add coverage for adding assets, deduping, unignoring, empty-account adds, and event emission (src/MultichainAssetsController/MultichainAssetsController.test.ts).
• Multichain Balances:
  • Balance Update Logic: On MultichainAssetsController:accountAssetListUpdated, populate balances for new assets and set balance to { amount: '0', unit: '' } when snap returns no balance (uses accounts map to track added assets).
  • Tests: Add tests for zero-balance behavior and existing/empty state updates (src/MultichainBalancesController/MultichainBalancesController.test.ts).
• Changelog: Document addAsset addition in packages/assets-controllers/CHANGELOG.md.

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[salimtb]

this should be an array of assetIds since we want to support selecting and adding multiple assets. I also think the function name should be addAssets.

[juanmigdr]

In the current implementation in mobile assets are added in a loop 1 by 1. I can change the implementation. Should I also rename the function to addAssets? Or should we have separate functions and if so in which case do we need addAsset (singular)

[Prithpal-Sooriya]

Good call.
If we can add multiple at the controller level, this should reduce state updates and computations. (Update all at once instead of one at a time).

In favour of renaming this if not yet used on clients.

[cursor]

Bug: Bug

The balance update logic has two main issues: it prevents existing asset balances from refreshing with new snap data, potentially leading to stale values or incorrect zeroing of assets. Also, new accounts don't initialize zero balances for assets not returned by the snap, causing inconsistencies.