vats/counter.js keeps its count in the vat's storage; the test checks
that it counts and that two counter vats count apart.
Running it after the greeter test hung: a FinalizationRegistry callback
in the vatAdmin, collecting an import, sent op:gc over the client's
WebSocket, and workerd forbids I/O outside a request. The vatAdmin's and
the vats' OCapN clients now run with enableImportCollection: false, so
imports go when their session does.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
