Fix var leak in LitEnum

Summary:
350bac2 added a VisitMut to LitEnum that skipped the `ty` field. This caused a Var leak that led to pyrefly crashing on the mypy_primer archinstall project.

This diff deep forces types before storing them in `LitEnum` to avoid leaking vars.

Fixes #3031.

Reviewed By: yangdanny97

Differential Revision: D99751901

fbshipit-source-id: f8691cfea089e55b315d05dd9806b8aff289a797

Author: rchen152

pyrefly/lib/alt/class/enums.rs

@@ -380,7 +380,7 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                 Lit::Enum(Box::new(LitEnum {
                     class: enum_.cls.clone(),
                     member: name.clone(),
-                    ty: ty.clone(),
+                    ty: self.solver().deep_force(ty.clone()),
                 }))
                 .to_implicit_type(),
             )

pyrefly/lib/test/enums.rs

@@ -1015,3 +1015,30 @@ class Planet(float, Enum):
 assert_type(Planet.MERCURY.value, float)
     "#,
 );
+
+fn frozen_enum_members_env() -> TestEnv {
+    TestEnv::one(
+        "foo",
+        r#"
+from enum import Enum
+from typing import Self
+class E(Enum):
+    A = frozenset({1})
+    B = frozenset({2})
+    @classmethod
+    def from_ord(cls) -> list[Self]:
+        return [v for v in cls]
+    "#,
+    )
+}
+
+testcase!(
+    test_frozen_enum_members_cross_module_iteration,
+    frozen_enum_members_env(),
+    r#"
+from foo import E
+def f() -> None:
+    xs = E.from_ord()
+    _ = [x for x in xs if x != E.A]
+    "#,
+);