chore(tests): replace aws-sdk-client-mock-vitest with local matcher

[svozza]

Summary

Replace aws-sdk-client-mock-vitest with a local toReceiveCommandWith matcher, removing the dependency compatibility blocker identified in #5655. The Vitest upgrade and its separate Assertion typing fix remain in that PR.

Changes

• Implement and register toReceiveCommandWith alongside the existing custom matchers in setupEnv.ts, preserving typed assertions, partial matching, asymmetric matcher support, negation, and failure diagnostics.
• Remove the dependency and unused snippet import, and update the documentation recommendation. Existing test assertions remain unchanged.
• Add unit and type tests. All 12 matcher tests pass, with every statement, function, and branch in the new matcher covered. Workspace type checks and the full pre-push suite of 3,718 tests pass with 100% coverage for the configured source files.

Issue number: closes #5692

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Disclaimer: We value your time and bandwidth. As such, any pull requests created on non-triaged issues might not be successful.