feat(derive): require form parameter for form handles

Emit handle-form facts from slhx-build and have #[slhx::handler] reject generated form handlers that do not accept slhx::Form<_>. Cover the boundary with compile-fail fixtures.

req: form/004

req: form/006

req: test/003

slhx-build/src/lib.rs

@@ -515,6 +515,9 @@ fn __slhx_attr(tag: &str, attr: &str) -> Option<::std::string::String> {
             let res = &form.resource;
             out.push_str(&format!("form\t{}\t{}\t{}\n", res.symbol, res.ident, res.id));
         }
+        for (handle_ident, form_ident) in &self.handle_forms {
+            out.push_str(&format!("handle_form\t{handle_ident}\t{form_ident}\n"));
+        }
         for res in self.atoms.values() {
             out.push_str(&format!("atom\t{}\t{}\t{}\n", res.symbol, res.ident, res.id));
         }
@@ -914,6 +917,7 @@ mod tests {
         let syms = std::fs::read_to_string(out.join("slhx.syms")).unwrap();
         assert!(syms.contains("atom\t"));
         assert!(syms.contains("\tfilter\t"));
+        assert!(syms.contains("handle_form\tcreate\tnew_todo\n"));
 
         let _ = std::fs::remove_dir_all(&base);
     }