@apollo/server-integration-testsuite vitest version

Howdy 👋

I've just come fresh off overhauling some dependencies for https://github.com/apollo-server-integrations/apollo-server-integration-koa aaaaaand

I'd really love to drop Jest because all my current OSS projects and my work projects have moved on to Vitest. Would we entertain the idea of shipping a Vitest version of this lib?

Initial thoughts were `@apollo/server-integration-testsuite/vitest` entrypoint with some copy 🍝 of the existing and moving out shared logic into shared files but I understand if you don't want to maintain two lots of the same thing.

Keen to hear your thoughts!

Start by inspecting the existing @apollo/server-integration-testsuite entrypoint and its Jest-specific test setup. Assess whether shared logic can support a proposed /vitest entrypoint without duplicating maintenance. Done means the project has agreed on an approach and, if accepted, provides a working Vitest-compatible version.

Written by the indexing model from the issue text.