feat(build): type generated event constants

Generate EventName constants for data-slhx-on metadata and exercise them through typed event emission in techdemo.

req: codegen/006

slhx-core/src/lib.rs

@@ -186,6 +186,41 @@ impl core::fmt::Display for CssClass {
     }
 }
 
+/// A generated, checked event token.
+/// req: codegen/006
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
+pub struct EventName {
+    name: &'static str,
+}
+
+impl EventName {
+    pub const fn new(name: &'static str) -> Self {
+        Self { name }
+    }
+
+    pub const fn as_str(self) -> &'static str {
+        self.name
+    }
+}
+
+impl AsRef<str> for EventName {
+    fn as_ref(&self) -> &str {
+        self.name
+    }
+}
+
+impl From<EventName> for String {
+    fn from(event: EventName) -> Self {
+        event.name.to_string()
+    }
+}
+
+impl core::fmt::Display for EventName {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.write_str(self.name)
+    }
+}
+
 /// A small displayable list of generated CSS class tokens for hemplate `+class`.
 /// req: style/003
 #[derive(Clone, Debug, Eq, PartialEq, Hash)]