Use analytic springs and instrument resize barriers

Share a stable damped oscillator solver across scalar and rectangle animations while preserving retarget and explicit no-crossing presentation policies. Add deterministic traces, scrolling and zoom continuity coverage, and pause-aware advancement.

Measure resize barrier and handoff timing behind resize-metrics, expose the feature through the release installer, and wait for the intended backend in isolated portal tests.

compositor/src/main.rs

@@ -22,6 +22,8 @@ mod presentation;
 mod private_client;
 mod reload;
 mod render;
+#[cfg(feature = "resize-metrics")]
+mod resize_metrics;
 mod resize_transaction;
 mod session_lock;
 mod shell_control;
@@ -143,6 +145,9 @@ fn main() -> Result<(), Box<dyn Error>> {
         }
     });
 
+    #[cfg(feature = "resize-metrics")]
+    state.resize_metrics.dump();
+
     runner.borrow_mut().stop();
     if let Some(child) = &mut child {
         terminate_child(child);