chore: migrate core (autocomplete) tests to vitest

[uinstinct]

Description

As part of our migration of tests inside core from jest to vitest, this PR:

• migrates the tests in the autocomplete directory.
• introduces vitest.global-setup and vitest.setup

related to CON-2030

Checklist

• [] I've read the contributing guide
• [] The relevant docs, if any, have been updated or created
• [] The relevant tests, if any, have been updated or created

Screenshots

[ For visual changes, include screenshots. Screen recordings are particularly helpful, and appreciated! ]

Tests

[ What tests were added or updated to ensure the changes work as expected? ]

[cubic-dev-ai[bot]]

Your cubic subscription is currently inactive. Please reactivate your subscription to receive AI reviews and use cubic.

[netlify[bot]]

✅ Deploy Preview for continuedev canceled.

Name	Link
🔨 Latest commit	33d3f5ab187130dd67860fe5a892dacecab9ae3e
🔍 Latest deploy log	https://app.netlify.com/projects/continuedev/deploys/6850fa3af9093b0008f9bad7

[recurseml[bot]]

⚠️ Only 5 files will be analyzed due to processing limits.

[recurseml[bot]]

😱 Found 1 issue. Time to roll up your sleeves! 😱