test(derive): close second mutation shard

Match public Form<T> paths with one unambiguous segment pattern and record clean hemx-derive shard 2/8 proof.

req: derive_handler/004

req: test/022

req: test/023

hemx-derive/src/lib.rs

@@ -289,22 +289,13 @@ fn form_model_type(ty: &Type) -> Option<Type> {
     let Type::Path(path) = ty else {
         return None;
     };
-    let mut segments = path.path.segments.iter();
-    let first = segments.next()?;
-    let last = path
-        .path
-        .segments
-        .last()
-        .expect("path has at least one segment");
-    let path_is_form = if path.path.segments.len() == 1 {
-        first.ident == "Form"
-    } else {
-        first.ident == "hemx" && last.ident == "Form"
+    let segments = path.path.segments.iter().collect::<Vec<_>>();
+    let form = match segments.as_slice() {
+        [form] if form.ident == "Form" => form,
+        [hemx, .., form] if hemx.ident == "hemx" && form.ident == "Form" => form,
+        _ => return None,
     };
-    if !path_is_form {
-        return None;
-    }
-    let PathArguments::AngleBracketed(args) = &last.arguments else {
+    let PathArguments::AngleBracketed(args) = &form.arguments else {
         return None;
     };
     args.args.iter().find_map(|arg| match arg {