Create automated Python test framework

[DeflateAwning]

• Expand on the work in CalgaryToSpace/CTS-SAT-1-OBC-Firmware#4, and create a pytest-based test system for issuing commands and get their response, over UART.
• Set this up such that the tests can be triggered from within VS Code.

First tests to create:

1. Hello world
2. Echo back the command args
3. "Get random bytes from the OBC" command - take special care when receiving null bytes
4. Something which tests the "delay milliseconds" and "current uptime" timer info.

[DeflateAwning]

Add even simpler tests:

1. test_always_passes, which just asserts true. Good for checking that Pytest is working at all.
2. test_can_open_connection, which just tests that the connection can be opened.

Those two will be helpful for checking if lots of the tests start failing ever