chore: Migrate test fixture to messenger

[Gudahtt]

Explanation

A test fixture used by the package @metamask/profile-sync-controller has been migrated to use the new @metamask/messenger package, in praration for the Messenger being removed from @metamask/base-controller.

References

Relates to #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

Switches the contact-syncing test fixture to use @metamask/messenger with namespaced Messenger and updated types.

• Tests (contact syncing):
  • Replace @metamask/base-controller Messenger with @metamask/messenger Messenger in __fixtures__/test-utils.ts.
  • Add MockAnyNamespace typing and initialize Messenger with MOCK_ANY_NAMESPACE.
  • Update generic types (ActionConstraint, EventConstraint) and imports to align with @metamask/messenger API.

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[Gudahtt]

I've labelled this as no-changelog because it only impacts a test fixture. No functional changes for the package.