rework weakref (RustPython#6916)

* Replace WeakListInner with inline atomic weakref list and stripe locks

Remove heap-allocated WeakListInner (OncePtr<PyMutex<WeakListInner>>).
WeakRefList now holds two inline atomic pointers (head, generic).
PyWeak.parent replaced with wr_object pointing directly to referent.
Add weakref_lock module with AtomicU8 spinlock array for thread safety.
Rewrite upgrade/clear/drop_inner/count/get_weak_references with stripe lock.
Make Pointers methods public in linked_list.rs.
Remove expectedFailure from test_subclass_refs_dont_replace_standard_refs.

* Auto-format: cargo fmt --all

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: youknowone

.cspell.dict/cpython.txt

@@ -192,6 +192,7 @@ venvwlauncher
 venvwlaunchert
 wbits
 weakreflist
+weakrefobject
 webpki
 withitem
 withs

Lib/test/test_weakref.py

@@ -1079,7 +1079,6 @@ def __call__(self):
         self.assertIsNone(mr())
         self.assertTrue(mr.called)
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON
     def test_subclass_refs_dont_replace_standard_refs(self):
         class MyRef(weakref.ref):
             pass

crates/common/src/linked_list.rs

@@ -333,15 +333,15 @@ impl<T> Pointers<T> {
         }
     }
 
-    const fn get_prev(&self) -> Option<NonNull<T>> {
+    pub const fn get_prev(&self) -> Option<NonNull<T>> {
         // SAFETY: prev is the first field in PointersInner, which is #[repr(C)].
         unsafe {
             let inner = self.inner.get();
             let prev = inner as *const Option<NonNull<T>>;
             ptr::read(prev)
         }
     }
-    const fn get_next(&self) -> Option<NonNull<T>> {
+    pub const fn get_next(&self) -> Option<NonNull<T>> {
         // SAFETY: next is the second field in PointersInner, which is #[repr(C)].
         unsafe {
             let inner = self.inner.get();
@@ -351,15 +351,15 @@ impl<T> Pointers<T> {
         }
     }
 
-    const fn set_prev(&mut self, value: Option<NonNull<T>>) {
+    pub const fn set_prev(&mut self, value: Option<NonNull<T>>) {
         // SAFETY: prev is the first field in PointersInner, which is #[repr(C)].
         unsafe {
             let inner = self.inner.get();
             let prev = inner as *mut Option<NonNull<T>>;
             ptr::write(prev, value);
         }
     }
-    const fn set_next(&mut self, value: Option<NonNull<T>>) {
+    pub const fn set_next(&mut self, value: Option<NonNull<T>>) {
         // SAFETY: next is the second field in PointersInner, which is #[repr(C)].
         unsafe {
             let inner = self.inner.get();