Creating an SKDB instance as a worker causes JS to hang

[Greg Sexton]

Repro:

import { createSkdb } from "skdb";
const db = await createSkdb({ asWorker: true });

If you change asWorker to false the node process will exit cleanly, otherwise it hangs.

The skdb type has a closeConnection method. We should probably change this to close() which should close any conns, other resources, and the worker if needed.

[Greg Sexton]

This is a low hanging one if someone fancies a quick win.