Check if tracker initialised correctly

[ElliottKasoar]

Similar to the discussions in #316 and #343, there can be issues in setting up the carbon tracker (e.g. NVML library mismatches), which mean the tracker is not set up correctly, but this does not raise an error until attempting to start a task.

We should check the tracker is set up, and if not, raise an error informing users of this, so they can either resolve the issue, or disable tracking.