Miscellaneous improvements

[eugenioLR]

Other improvements, and inconsistencies observed while using the code

Infrastructure & Improvements

• Remove leftover Enum from BranchOperator, switch to dict-registry or split into different operators
• Add parameter discovery interfaces (list_operator_parameters or include them in the original function)
• Track stagnation tracking for plots.
• Add patience tolarance to detect convergence.
• Refactor DE: split mutation (donor generation) from binomial crossover. We get new crossover operators for free.
• Add diversity‑based stopping conditions. (research)
• Allow *FromLambda classes to be used as decorators (e.g. @OperatorFnDef)
• Provide opinionated default plots (convergence, diversity, parameter evolution)
• Extract population‑shaping methods (take_selection, join, repeat, …) as free functions to reduce bloat in Population.
• Advanced statistics helpers: paired tests, confidence intervals, effect sizes (optional, nice to have)