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? ]