feat: add vitest-dev/vscode

[hi-ogawa]

This PR adds Vitest VS Code extension https://github.com/vitest-dev/vscode.

Little summary of the repo and tests:

• Currently extension has own modified version of @vitest/ws-client https://github.com/vitest-dev/vscode/blob/85aa7edfce24914bee6a849e61d935e8f0b97bb2/src/pure/watch/ws-client.ts and uses it to communicate with Vitest CLI spawned by --api (though this might change in the future by feat: use Vitest public API instead of Vitest CLI vscode#253)
• pnpm test (added in feat: switch to vs code tests vscode#262) only tests internal utilities, so it doesn't really exercise Vitest feature.
• pnpm test-e2e (will be added in test: setup vscode-e2e vscode#276) runs a simple sample with extensions, so this will exercise both extension's ws-client implementation and Vitest CLI.

I think we can wait this PR until E2E is setup on vscode extension repo, but I just wanted to explore ecosystem-ci beforehand.

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[hi-ogawa]

I verified the CI on my fork:
https://github.com/hi-ogawa/vitest-ecosystem-ci/actions/runs/8135294958/job/22229582638#step:8:92

I doesn't look flaky on vscode repo's PR vitest-dev/vscode#276, but I just saw one failure in https://github.com/hi-ogawa/vitest-ecosystem-ci/actions/runs/8135259673/job/22229493916#step:8:201
Hopefully, it's not bothering right now, so I think we can go with this. If it turns out to be flaky, I'll investigate it.

Actually it looks flaky. For now, I added retry and it looks better, but I might need to dig into this.