[Python] Add checks when parsing RegressionStateScenes.regression-tests file

[fredroy]

On the SOFA codebase, the regression was crashing for FEMBAR_ShewchukPCGLinearSolver.scn because the RegressionStateScenes.regression-tests is missing an argument (nb of steps) for this scene. Apparently the C++ version is not bothered....

[alxbilger]

Check for conflicts with #118. I made this PR also to handle the FEMBAR_ShewchukPCGLinearSolver scene.

[fredroy]

Akshually, it is #118 which makes FEMBAR_ShewchukPCGLinearSolver.scn regression test crash 🫢
It crashes because FEMBAR_ShewchukPCGLinearSolver has 4 fields (instead of the required 5)
and python throws an exception here

            if len(values) < 2:
                helper.writeWarning(f"Cannot evaluate steps from line: {line}. Default value {steps} will be used instead.")
            else:
                steps = int(values[1]) <---

because values[1] in this case instead of being a number of steps (as it should be) is an epsilon (1e-8). Python throws ValueError exception in this case.

[alxbilger]

I suggest to go with json in the future