Refactor

[xin-huang]

Hello @nomis-c

Please refactor the command-line interface to follow the structure used in sai/main.py.
Each subcommand should be moved to a separate module, as illustrated in sai/parsers.

Thank you.

[xin-huang]

• Add unit tests (using pytest) for each parser module
• Replace utils.py here with utils.py from sai

[nomis-c]

I have updated utils.py and added the tests for all parser modules. Running pytest shows no errors, and all tests are passing (except for the one that's intentionally skipped). I'm not 100% sure if the new utils.py is as you intended it to be, so it would be helpful if you could take a look at it when you have time.