Support DuckDB nightly builds

There should be a way to at least test Node Neo with DuckDB nightly builds. Maybe such builds of Node Neo should be published as well. (If they were, the [nightly installation page for Node](https://duckdb.org/docs/installation/?version=main&environment=js) could be updated to point to Neo.)

The former should be straightforward to build using a `nightly` branch. The latter could presumably be accomplished with some GitHub Actions that run on a schedule. But maintaining the latter, and troubleshooting broken builds, might be too much work given current bandwidth (i.e. just me, in my spare time).