test: run messenger on Vitest

[cryptodev-2s]

Explanation

Moves @metamask/messenger to Vitest.

References

• Part of the Jest to Vitest migration, see test: add Vitest alongside Jest #10546 for the shared setup

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
  • Not applicable, test only change. Carries the no-changelog label.
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them
  • None.

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Note

Low Risk
Test-only and config changes with no runtime library behavior changes; main risk is CI or local test workflow regressions.

Overview
Migrates @metamask/messenger from Jest + Tstyche to Vitest as part of the broader Jest→Vitest effort. Production code is unchanged; only test tooling and configs move.

The package drops jest.config.cjs and adds vitest.config.js (shared package base, typecheck enabled, same coverage thresholds as before). package.json scripts now call vitest only—no separate test:types / Tstyche step. Unit tests use vi instead of jest; type tests in Messenger.test-d.ts use @ts-expect-error instead of Tstyche’s expect().type assertions. Build/tsconfig excludes **/*.test-d.ts instead of *.tst.ts, and Jest types are removed from the package tsconfig. @metamask/messenger is removed from the Jest test-runner package map so CI runs it via Vitest.

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