Taming Row Height and Spacing Jumps in SwiftUI List with a Custom Layout

The declarative expression of animation is one of SwiftUI's core strengths. But in some scenarios the result isn't always as smooth as we'd hope. A typical example: when the content height inside a `List` row changes dynamically — a subtitle going from empty to non-empty, or text changing its line count after an update — the system's built-in layout engine often fails to produce a continuous…