Export a design's timeline as a replayable command script (#1045)

timeline.export_script (and solidcraft-cli script) writes a design's history as a command script that solidcraft-cli eval replays into the same design, so a bug that only shows on one design becomes a one-file repro. timeline.add restores one stored feature with its id, names and references, through the same checks a design file gets when it opens.

Closes #886. SychPL's #1078 approached the same issue independently; thanks to both.

Co-authored-by: SychPL <SychPL@users.noreply.github.com>

crates/engine/src/tests.rs

@@ -729,8 +729,8 @@ fn hostile_params_never_panic() {
                     while let Some(&id) = ids.get(next.fetch_add(1, std::sync::atomic::Ordering::Relaxed)) {
                         for v in hostile_values() {
                             for k in keys {
-                                if k == "path" && id.starts_with("parameters.") {
-                                    continue; // parameter files: covered by their own tests (no stray files)
+                                if k == "path" && (id.starts_with("parameters.") || id == "timeline.export_script") {
+                                    continue; // parameter and script files: covered by their own tests (no stray files)
                                 }
                                 let mut s = Session::default();
                                 // A model with a sketch, a body and an active sketch, so most commands get far.