Fixed #35405 -- Converted get_cache_name into a cached property in FieldCacheMixin.

FieldCacheMixin is used by related fields to track their cached values.
This work migrates get_cache_name() to be a cached property to optimize
performance by reducing unnecessary function calls when working with
related fields, given that its value remains constant.

Co-authored-by: Simon Charette <charette.s@gmail.com>
Co-authored-by: Sarah Boyce <42296566+sarahboyce@users.noreply.github.com>
Co-authored-by: Natalia <124304+nessita@users.noreply.github.com>

tests/model_fields/test_mixins.py

@@ -0,0 +1,75 @@
+from django.db.models.fields.mixins import FieldCacheMixin
+from django.test import SimpleTestCase
+from django.utils.deprecation import RemovedInDjango60Warning
+from django.utils.functional import cached_property
+
+from .models import Foo
+
+
+# RemovedInDjango60Warning.
+class ExampleOld(FieldCacheMixin):
+    def get_cache_name(self):
+        return "example"
+
+
+class Example(FieldCacheMixin):
+    @cached_property
+    def cache_name(self):
+        return "example"
+
+
+class FieldCacheMixinTests(SimpleTestCase):
+    def setUp(self):
+        self.instance = Foo()
+        self.field = Example()
+
+    # RemovedInDjango60Warning: when the deprecation ends, replace with:
+    # def test_cache_name_not_implemented(self):
+    #   with self.assertRaises(NotImplementedError):
+    #       FieldCacheMixin().cache_name
+    def test_get_cache_name_not_implemented(self):
+        with self.assertRaises(NotImplementedError):
+            FieldCacheMixin().get_cache_name()
+
+    # RemovedInDjango60Warning.
+    def test_get_cache_name_deprecated(self):
+        msg = "Override ExampleOld.cache_name instead of get_cache_name()."
+        with self.assertWarnsMessage(RemovedInDjango60Warning, msg):
+            result = ExampleOld().cache_name
+        self.assertEqual(result, "example")
+
+    def test_cache_name(self):
+        result = Example().cache_name
+        self.assertEqual(result, "example")
+
+    def test_get_cached_value_missing(self):
+        with self.assertRaises(KeyError):
+            self.field.get_cached_value(self.instance)
+
+    def test_get_cached_value_default(self):
+        default = object()
+        result = self.field.get_cached_value(self.instance, default=default)
+        self.assertIs(result, default)
+
+    def test_get_cached_value_after_set(self):
+        value = object()
+
+        self.field.set_cached_value(self.instance, value)
+        result = self.field.get_cached_value(self.instance)
+
+        self.assertIs(result, value)
+
+    def test_is_cached_false(self):
+        result = self.field.is_cached(self.instance)
+        self.assertFalse(result)
+
+    def test_is_cached_true(self):
+        self.field.set_cached_value(self.instance, 1)
+        result = self.field.is_cached(self.instance)
+        self.assertTrue(result)
+
+    def test_delete_cached_value(self):
+        self.field.set_cached_value(self.instance, 1)
+        self.field.delete_cached_value(self.instance)
+        result = self.field.is_cached(self.instance)
+        self.assertFalse(result)