feat(assets-controllers): detect mUSD with zero balance on all paths

[salimtb]

Merge mUSD into the token list cache for WS/polling and append it to detection slices when the RPC/API omits zero balances. Extend Accounts API import to schedule mUSD on supported chains per poll. Single-call path already merged in prior work.

Made-with: Cursor

Explanation

References

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
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them