67d8ddca

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Mutation: suppress symmetric-function swaps via skip-calls-to config

Symmetric functions (max, min, set union, a majority predicate, ...) make
SwitchFunctionArguments produce equivalent mutants that no test can kill.
Since symmetry is a semantic property the plugin cannot detect, the operator
now reads a per-operator 'skip-calls-to' list of function names from its
config and skips swapping the arguments of any call to a listed function.
Names match either bare ('max') or fully qualified ('GHC.Base.max').

Adds the operatorExtraStrings config helper (+ test), switches the example's
symmetric majorityOf5Wrapper from a call-site DisableMutation annotation to
the new registry (nix/mutation.yaml), and documents the mechanism in the
surviving-mutation remediation guidance.