Tests: Test or remove runnableExamples in non-exported procs

[ee7]

PR #94 added some runnableExamples to a non-exported proc, which means that the examples don't run even if we were to add nim doc to the CI.

It would be nice to have:

• the benefits of having examples right next to the implementation of non-exported procs
• and keep those examples tested.

@ee7 wrote:

The alternatives that I'm aware of:

1. Remove the examples entirely, but then the documentation is less clear.
2. Turn the runnableExamples into doc comments, but then they're harder to test and thus keep in-sync with the code.
3. Move the examples into when isMainModule tests, and add nim c -r cli.nim to the CI workflow. This means that they're tested, but the documentation suffers because the examples aren't close to the func itself, and the test layout becomes more convoluted.
4. Move the examples into a new file in the tests directory. This requires using include cli (rather than import), or a short hack/macro to export non-exported procs for testing purposes.
5. Export the func, but that signals to the reader that the func is used outside the cli.nim file, which it isn't.