kwai: cli test for kwai-split

kwai-split - split an input dataset into train/validate/test datasets

We have tests for some of the higher-level functions these use, but none for the tools themselves. So, we're forced to test them manually.

It would be great to have some (even basic) tests for these. A python implementation using pytest would be best, but Bash would be alright too, given the tests are integrated with the CI pipeline.

Here are some testing ideas for each of these:

• kwai-split - I can create a small CSV file, accompanied by a ZIP file, constituting a dataset together. The test could verify that the tool produces the correct output files (with byte-for-byte comparison).

parent issue: cki-project/experimental/kwai#16 (closed)

Jira: CKI-7025