Swap Ava with node-core-tests

[eklem]

This will eventually lead to one less dependency if it works. (in 2024).
https://github.com/juliangruber/node-core-test/

Create a branch and check if it works. If ok, publish it as a next tag and do the same for batr-example.

[eklem]

v16.x of nodejs is outdated, so it should work withtout this library.
NodeJS release plan

NodeJS test runner