Replace cargo-cranky with workspace lints (#4413)

Replace `cargo-cranky` (which has served us well) with workspace lints

crates/egui_demo_app/src/main.rs

@@ -1,6 +1,7 @@
 //! Demo app for egui
 
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+#![allow(rustdoc::missing_crate_level_docs)] // it's an example
 #![allow(clippy::never_loop)] // False positive
 
 // When compiling natively: