By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Mutation: fix SwitchFunctionArguments double-firing on parenthesised applications collectApp peeled an enclosing HsPar, so a parenthesised application like succ (div a b) was matched both at the parenthesis node and at the inner application node, emitting the same swap mutation twice. The walker already recurses into an HsPar with instrumentLExpr (which re-runs every operator), so stopping at the HsPar leaves the inner application as the single firing site. Adds Example.SwitchArgsLib.parenDivide as a regression case (its golden now shows exactly one swap) plus a killing spec.