refactor(techdemo): render test metric with hemplate

Replace the techdemo generated-slot test's inline raw HTML payload with a hemplate partial-rendered view.

req: html_safety/002

req: view/001

examples/techdemo/src/lib.rs

@@ -4,15 +4,22 @@ pub mod ui {}
 #[cfg(test)]
 mod tests {
     use super::ui;
+    use hemplate::Hemplate;
     use slhx::{IntoEffect, SafeHtml};
     use slhx_test::inspect;
 
+    #[derive(Hemplate)]
+    #[hemplate = "partials"]
+    struct FastMetric {
+        label: &'static str,
+    }
+
     // req: examples/001 req: codegen/002 req: public_api/001
     #[test]
     fn techdemo_uses_generated_slots_for_multi_target_updates() {
         fn update() -> impl IntoEffect {
             (
-                ui::control_center::slots::hero_metrics.html(SafeHtml::trusted("<b>fast</b>")),
+                ui::control_center::slots::hero_metrics.html(render_fast_metric("fast")),
                 ui::control_center::slots::notice.text("typed"),
             )
         }
@@ -22,6 +29,15 @@ mod tests {
         assert!(batch.has_slot(ui::control_center::slots::notice));
     }
 
+    fn render_fast_metric(label: &'static str) -> SafeHtml {
+        // req: html_safety/002 req: view/001
+        SafeHtml::trusted(
+            FastMetric { label }
+                .render()
+                .expect("techdemo fast metric renders"),
+        )
+    }
+
     // req: examples/001 req: form/002 req: codegen/003
     #[test]
     fn techdemo_exports_form_and_interaction_handles() {

examples/techdemo/templates/partials/fast_metric.heml

@@ -0,0 +1 @@
+<b>{+ self.label +}</b>