feat: SeedlessOnboardingController: migrate messenger

[matthiasgeihs]

Explanation

Migrate messenger for SeedlessOnboardingController

References

#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 SeedlessOnboardingController to the new @metamask/messenger API and base-controller/next, and renames state metadata flag from anonymous to includeInDebugSnapshot.

• Seedless Onboarding Controller:
  • Migrate from @metamask/base-controller messenger to @metamask/messenger (SeedlessOnboardingController.ts, types.ts).
  • Switch imports to @metamask/base-controller/next.
  • Rename state metadata property anonymous → includeInDebugSnapshot and update usages.
• Tests:
  • Replace legacy messenger mocks with new @metamask/messenger-based root/restricted messengers; update fixtures and test helpers.
  • Update deriveStateFromMetadata calls to use includeInDebugSnapshot.
• Docs/Meta:
  • Update CHANGELOG.md with breaking changes notes.
  • Update README dependency graph (add seedless_onboarding_controller --> messenger, and show new edge for eip_7702_internal_rpc_middleware).
• Dependencies:
  • Add @metamask/messenger dependency.

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