GH-104787: use managed weakrefs in _asyncio

[kumaraditya303]

• Issue: Optimize and reduce memory usage for asyncio.Task and others #104787

[gvanrossum]

I'm not sure who is an expert in these APIs. Maybe @markshannon can review?

[kumaraditya303]

I'm not sure who is an expert in these APIs.

Not much to review, see

cpython/Modules/_testcapi/heaptype.c

Lines 861 to 868 in 2ef1dc3

	static PyType_Spec HeapCTypeWithManagedWeakref_spec = {
	"_testcapi.HeapCTypeWithManagedWeakref",
	sizeof(PyObject),
	0,
	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_MANAGED_WEAKREF,
	HeapCTypeWithManagedWeakref_slots
	};

as example of usage