feat: add optional error codes to `networkError`

[GerkinDev]

Closes #365

The expected bundle size seems very constraining, and I did not find a way to reduce it below 3Kb without impacting readability or doing deeper reconf/refactoring.

Also, I had issues installing the dev dependencies since I'm using node 20 and bundlesize relies on [email protected] which in turn relies on iltorb@^2.4.3 that is deprecated and using legacy node-gyp headers. Somehow, I fixed it locally, but specifying the node version you use either in the readme or in an .nvmrc file would have helped.