Distance coefficient power parameter in QEC scheme

[msoeken]

This PR extends the formula template for QEC logical error rate formulas from:

$$ a \left(\frac{p}{p_{\mathrm{th}}}\right)^{\frac{d+1}{2}} $$

to

$$ a d^k \left(\frac{p}{p_{\mathrm{th}}}\right)^{\frac{d+1}{2}} $$

where $k$ is the new distance coefficient power discussed in arXiv:2411.10406, Section III.B, page 25.

For $k = 0$, the default, the formula remains unchanged compared to the current one. However, changing $k$ to other values allows to model a different error correction behavior, as motivated by the paper.

The parameter is called distance_coefficient_power or distanceCoefficientPower in the JSON parameter. It is also added to the Python RE parameter utility structure (together with max_code_distance which was absent so far).