Consider updating sisteransi to v2 #609

Three months ago, sisteransi released v2.0.0, which ported the package to ESM with no API changes. Moving to ESM enables tree-shaking, which can reduce consumers' bundle size, and removes the CJS interop/loader helpers for ESM-only projects. In one of my projects, I already bumped sisteransi via an override in pnpm-workspace.yaml, but it would be nice if @clack/core could be updated to 2.0.0 directly.