test(examples): render hemplate views into buffers

Use hemplate render_into in public examples and example tests instead of the string-returning render helper, preserving SafeHtml wrapping only at the explicit effect boundary.

req: view/001

req: html_safety/002

examples/kanban/src/lib.rs

@@ -45,11 +45,11 @@ mod tests {
 
     fn render_empty_board() -> SafeHtml {
         // req: html_safety/002 req: view/001
-        SafeHtml::trusted(
-            BoardColumns { columns: Vec::new() }
-                .render()
-                .expect("kanban board test view renders"),
-        )
+        let mut html = String::new();
+        BoardColumns { columns: Vec::new() }
+            .render_into(&mut html)
+            .expect("kanban board test view renders");
+        SafeHtml::trusted(html)
     }
 
     fn selector(value: &str) -> Selector {