Improve tests: include frequency domain monitors and wake extrapolation

[elenafuengar]

In order to improve coverage of the latest functionalities, the following missing tests are required to be added to the pytest nightly execution:

• Test frequency domain field monitors: UNIT / E2E, based on example 005_CPU_with_field_monitor.py
• Test counter-rotating beam output: UNIT / E2E, based on example 006_CPU_counter_moving_field_monitor.py
• Test wake extrapolation wrapper of IDDEFIX based on notebook 004_Wakefield_simulation_and_extrapolation.ipynb

Documentation https://wakis.readthedocs.io should be updated to explain the frequency domain field monitors class field_monitors.py computation and usage.

Help is more than welcome if someone wants to give it a try 🫶