Upgrade and fix eslint config

[rotu]

Previously, npm install; npm run lint would fail. Now it succeeds.

This involved a couple changes:

1. switch from eslint legacy to flat config
2. bump some plugins, including removing some straggling references to the unmaintained eslint-plugin-node in favor of its sucessor eslint-plugin-n and removing eslint-plugin-import, which is unused and incompatible with eslint 9.
3. Use the recommended config for typescript-eslint.
4. Turn off the rule @typescript-eslint/no-require-imports, which currently fails on parts of the codebase.