feat(build): emit checked param tokens

Generate ParamName constants for handle data parameters so public code can refer to checked param metadata instead of stringly typed names.

req: codegen/003

slhx/src/lib.rs

@@ -50,7 +50,7 @@ pub mod prelude {
     pub use slhx_core::{
         navigate, push, redirect, replace, Atom, BuildFingerprint, ComponentRef, CssClass,
         CssClasses, Effect, EventName, Form, FormModel, FormValue, Handle, IntoEffect, KeyedSlot,
-        Slot,
+        ParamName, Slot,
     };
     pub use crate::{render_html, RenderKeyedSlotExt, RenderSlotExt};
     pub use slhx_derive::{app, component, form, handler, surface};