By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Mutation: RemoveClause operator + operator sum type Add a RemoveClause function-declaration mutation operator that removes one equation from a multi-clause function binding by guarding the clause with ifMutation, so the clause falls through (or hits a non-exhaustive MatchFail) when active. Model operators as a sum of kinds: MutationOperator carries the shared name and description plus an operatorKind that is either an ExpressionOperator (the original LHsExpr operators) or a FunctionDeclarationOperator (operating on a binding's MatchGroup). RemoveClause lives in its own auto-discovered module and is enabled/disabled uniformly via the registry.