refactor: migrate assets controllers messenger

[mikesposito]

Explanation

This PR migrates all remaining assets controllers to @metamask/messenger instead of @metamask/base-controller. This is part of a larger effort to migrate all controllers to use @metamask/messenger.

References

• Related to Implement messenger delegation #5626

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

Migrates remaining assets controllers and tests to the new @metamask/messenger API and base-controller/next metadata, updating messaging, types, snapshots, and changelog.

• Controllers:
  • Migrate MultichainAssetsController, MultichainBalancesController, NftDetectionController, RatesController, and TokenSearchDiscoveryDataController from RestrictedMessenger to @metamask/messenger (messagingSystem → messenger).
  • Update types to use Messenger<...> and adopt @metamask/base-controller/next where applicable.
  • Replace state metadata anonymous with includeInDebugSnapshot; add StateMetadata typing.
  • Swap publish/subscribe/call sites to the new messenger API; adjust event publishing (e.g., ${name}:pollingStarted|Stopped).
• Tests:
  • Rework test messengers to use root Messenger with namespace/delegate; replace helper extraction types with MessengerActions/MessengerEvents.
  • Update deriveStateFromMetadata calls to use includeInDebugSnapshot.
• Changelog:
  • Consolidate and expand the BREAKING change note to reflect migration to @metamask/messenger and reference related PRs.
• Misc:
  • Minor ESLint threshold adjustments in eslint-warning-thresholds.json.

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[mcmire]

One thing that Cursor noticed.

[mcmire]

Hmm, it does seem that we need a parent option here.