Adapt Echidna training

We need to adapt the Echidna training to:
- Use https://github.com/crytic/properties/blob/main/contracts/util/PropertiesHelper.sol, and integrate recommendations regarding the `properties` repo
- Make it compatible with medusa

Start with the Echidna training materials and compare their current guidance with PropertiesHelper.sol in the properties repository. Review the properties-repository recommendations and determine the changes needed for Medusa compatibility; the training is done when both requirements are reflected clearly and the relevant examples remain usable.

Written by the indexing model from the issue text.