flutter-perf-lists-and-scrolling

Use for janky scroll, slow first paint of long lists, or thousands of widgets built at once. Improves scrolling and list performance in Flutter: replaces eager ListView(children: data.map(...).toList()) with ListView.builder, GridView.builder or sliver builders for large item histories, and evaluates itemExtent, prototypeItem and itemExtentBuilder to cut layout work. Do not use for small fixed lists, and not for per-item rebuild scope (flutter-perf-build- and-rebuild).