A failed feature has a mark of its own in the timeline and the Feature History (#972) (#1180)

A failed feature gets its own mark in the timeline and Feature History, distinct from warnings, with tests.

crates/ui-egui/src/lib.rs

@@ -59,6 +59,8 @@ mod menu_tests;
 #[cfg(test)]
 mod surface_clamp_tests;
 #[cfg(test)]
+mod timeline_marks_tests;
+#[cfg(test)]
 mod status_tests {
     #[test]
     fn the_status_bar_names_commands_by_label() {