Feature/cli migrate with testing

[arekouzounian]

• refactored the langs and run commands to use the updated API
• added a timeout option to the root command for adjusting client timeouts
• refactored the Client object to take in a Requester, for use in mocks
• created some mock tests as well as some basic tests against a mock HTTP server

[arekouzounian]

Going to flag this as a draft right now; this is my first attempt at using Gomock so I'm open to any feedback on how I can improve the tests and/or make them more idiomatic.

I could also implement some more blackbox tests that run against the actual deployment to check for expected behavior.