- added a first draft of an implementation of the Plant Propagation Algorithm ([PPA](https://thomasweise.github.io/moptipy/moptipy.algorithms.so.html#module-moptipy.algorithms.so.ppa))
- added the new [Op1SwapTryN](https://thomasweise.github.io/moptipy/moptipy.operators.permutations.html#module-moptipy.operators.permutations.op1_swap_try_n) operator, which is a unary operator with step size, for permutations