[FEATURE] Add built-in data logging and plotting utilities to the pytest infra

**Is your feature request related to a problem? Please describe.**
When debugging a firmware or test issue, it's common to add print statements to the firmware (or in the test code) to observe signal data changing over time.

**Describe the solution you'd like**
I want infrastructure that supports logging any signals (tagged data, C variables, etc) the user selects over time. It could just produce a CSV (and maybe also a plot) for each test run.

Start by mapping the existing pytest infrastructure and how a test run exposes tagged data or C variables. Define the supported signal-selection interface and CSV or plot output before implementation; done means selected signals are captured over time and artifacts are produced for each test run.

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