Autotuner: Make flow variable detection more robust

[maliberty]

Subject

[Stage]: Other. Please describe below.

Describe the bug

In #2397 the check

            if key not in flow_variables:
                print(f"[ERROR TUN-0017] Variable {key} is not tunable.")
                sys.exit(1)

was disabled due to robustness issues.

Expected Behavior

Do not try to parse the tcl files directly and use a more generic mechanism to get the flow variables. #2393 might be relevant.

Environment

As above.

To Reproduce

Use the latest ORFS with the commented section of code re-enabled.

Relevant log output

No response

Screenshots

No response

Additional Context

No response