refactor: migrate MultichainNetworkController to @metamask/messenger

[cryptodev-2s]

Explanation

This PR migrates MultichainNetworkController to the new @metamask/messenger message bus, as opposed to the one exported from @metamask/base-controller.

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 MultichainNetworkController to the new @metamask/messenger, updates types/imports to @metamask/base-controller/next, renames metadata flag, and refactors tests and deps accordingly.

• MultichainNetworkController:
  • Migrate from RestrictedMessenger to new Messenger (@metamask/messenger), replacing messagingSystem.* with messenger.* calls.
  • Register/subscribe via messenger.registerActionHandler and messenger.subscribe; publish MultichainNetworkController:networkDidChange via new messenger.
• Types/Constants:
  • Switch imports to @metamask/base-controller/next.
  • Update MultichainNetworkControllerMessenger type to use Messenger and adjust allowed actions/events.
  • Rename metadata property anonymous to includeInDebugSnapshot in MULTICHAIN_NETWORK_CONTROLLER_METADATA and tests.
• Tests:
  • Refactor to construct root/child messengers (MOCK_ANY_NAMESPACE, delegate) and update spies/mocks accordingly.
• Dependencies/Docs:
  • Add @metamask/messenger dependency in package.json and reflect in README dependency graph.
  • Update changelog with breaking changes.

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