The mail list passed `onEndReached` and `onRefresh` as inline arrows,
so FlatList (a pure component) re-rendered on every render of the
screen, and without `strictMode` it then handed its cells a new render
function, so every mounted row re-rendered too. Each row also built a
fresh swipe `context` object and `onAction` closure, so its
`SwipeableRow` could never skip a render. Loading the next page while
scrolling flips `loading` and appends rows, re-rendering up to a couple
of hundred rows mid-fling.
- `onEndReached` and `onRefresh` are stable callbacks and FlatList runs
with `strictMode`, which the default React Native typings lack, so
`src/types/react-native-flatlist.d.ts` declares it
- each row is an `EmailListItem`, memoized on primitives and stable
callbacks, which builds its swipe context and callback once per row
- rows share one swipe callback that reads the current handler through
a ref, so rebuilding the handler no longer re-renders every row
