* Add ``Profile.necessary_coalition_size_to_break_irv_immunity``: necessary coalition size to break IRV immunity (for
each candidate different from the IRV-immune candidate, if one exists).
* Use this notion to improve the bound ``necessary_coalition_size_cm_`` for ``RuleCondorcetAbsIRV``,
``RuleCondorcetVtbIRV``, ``RuleExhaustiveBallot``, ``RuleICRV``, ``RuleIRV``, ``RuleIRVAverage``, ``RuleSmithIRV``,
``RuleTideman`` and ``RuleWoodall``.