chore(deps): upgrade atomico to v2 #324

Summary

Upgrade atomico from 1.x to 2.x in packages/atomico.

Part of the dependency cleanup series. Depends on #317 and #318.

Notes

Try to maintain backwards compatibility with atomico 1. If backcompat is not feasible, break backwards and document in changeset.

Affects @apollo-elements/atomico package. Also check @atomico/hooks compat.

Verification

• npm run build succeeds
• npm test passes
• Atomico package tests pass specifically