- Remove unused ui_println/ui_eprintln macros
- Add #[must_use] to CliLayer::real()
- Allow type_complexity in cli_layer tests

Take our tracing-based versions over main's reformatted print macros
and remove clippy allow attrs that are no longer needed.

Drop CliLayer and all `target: "user::stderr"` / `target: "user::stdout"`
usage. Former eprintln! calls now use tracing::error!/warn!/info! based
on semantics. Former println! calls use tracing::info!. Subscriber is a
single tracing_subscriber::fmt() with --verbose toggling debug level.