[ty] Pass down specialization to generic dataclass bases (#19472)

## Summary

closes https://github.com/astral-sh/ty/issues/853

## Test Plan

Regression test

crates/ty_python_semantic/src/types/class.rs

@@ -1668,16 +1668,16 @@ impl<'db> ClassLiteral<'db> {
         if field_policy == CodeGeneratorKind::NamedTuple {
             // NamedTuples do not allow multiple inheritance, so it is sufficient to enumerate the
             // fields of this class only.
-            return self.own_fields(db);
+            return self.own_fields(db, specialization);
         }
 
         let matching_classes_in_mro: Vec<_> = self
             .iter_mro(db, specialization)
             .filter_map(|superclass| {
                 if let Some(class) = superclass.into_class() {
-                    let class_literal = class.class_literal(db).0;
+                    let (class_literal, specialization) = class.class_literal(db);
                     if field_policy.matches(db, class_literal) {
-                        Some(class_literal)
+                        Some((class_literal, specialization))
                     } else {
                         None
                     }
@@ -1691,7 +1691,7 @@ impl<'db> ClassLiteral<'db> {
         matching_classes_in_mro
             .into_iter()
             .rev()
-            .flat_map(|class| class.own_fields(db))
+            .flat_map(|(class, specialization)| class.own_fields(db, specialization))
             // We collect into a FxOrderMap here to deduplicate attributes
             .collect()
     }
@@ -1707,7 +1707,11 @@ impl<'db> ClassLiteral<'db> {
     ///     y: str = "a"
     /// ```
     /// we return a map `{"x": (int, None), "y": (str, Some(Literal["a"]))}`.
-    fn own_fields(self, db: &'db dyn Db) -> FxOrderMap<Name, (Type<'db>, Option<Type<'db>>)> {
+    fn own_fields(
+        self,
+        db: &'db dyn Db,
+        specialization: Option<Specialization<'db>>,
+    ) -> FxOrderMap<Name, (Type<'db>, Option<Type<'db>>)> {
         let mut attributes = FxOrderMap::default();
 
         let class_body_scope = self.body_scope(db);
@@ -1747,7 +1751,14 @@ impl<'db> ClassLiteral<'db> {
                     let bindings = use_def.end_of_scope_bindings(place_id);
                     let default_ty = place_from_bindings(db, bindings).ignore_possibly_unbound();
 
-                    attributes.insert(place_expr.expect_name().clone(), (attr_ty, default_ty));
+                    attributes.insert(
+                        place_expr.expect_name().clone(),
+                        (
+                            attr_ty.apply_optional_specialization(db, specialization),
+                            default_ty
+                                .map(|ty| ty.apply_optional_specialization(db, specialization)),
+                        ),
+                    );
                 }
             }
         }