Implement more algorithms for zeta functions

[PhilippSchuette]

While being quite straightforward to implement, cycle expansion is not an optimal algorithm for the calculation of (dynamical) zeta functions. This is mainly due to the exponential growth of the number of closed geodesics as their length grows towards infinity.

Thankfully, other algorithms exist: [Bandtlow, Pohl, Schick, Weiße 2020] demonstrated how to calculate zeta functions in their representation as Fredholm determinants. Having such an alternative algorithm available within the PyZeta project could on the one hand enable the calculation of resonances significantly further into the left halfplane. On the other hand one could then verify both methods against each other to gain additional confidence in the validity of the results.