feat(core): format handles for templates

Implement Display for generated Handle<T> values and migrate example view data to carry handles directly instead of raw handle id numbers for dynamic handle attributes.

req: public_api/001

req: public_api/002

slhx-core/src/lib.rs

@@ -896,6 +896,12 @@ impl<I> Handle<I> {
     }
 }
 
+impl<I> core::fmt::Display for Handle<I> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        self.id.id.fmt(f)
+    }
+}
+
 pub trait FormValue {}
 
 impl<T> FormValue for T where T: std::str::FromStr {}