docs: add vitest-evals example and guide

[mhart]

No description provided.

[astrobot-houston]

Thanks for the contribution! We're closing this PR and moving the conversation to the discussion: #247

We've moved to a model where bugs and feature proposals are discussed in issues/discussions before code review, so the community can help prioritize and shape the work. Your branch is linked from the new thread so the implementation isn't lost — please join us there to continue the conversation.

— astrobot 🤖

[mhart]

This is up to date now. As an aside: codebase needs a formatting run (blueprints/*.md, packages/mongodb/src/*.ts)

[FredKSchott]

This is now live in the shipped docs: https://flueframework.com/docs/guide/evals/ Thanks again for the contribution!