DEPR: enforce deprecations on DateOffset methods (#48685)

* DEPR: enforce deprecations on DateOffset methods

* mypy fixup

* fix asv

* move whatsnew

Author: jbrockmendel

asv_bench/benchmarks/tslibs/offsets.py

@@ -71,11 +71,8 @@ def setup(self, offset):
         self.date = datetime(2011, 1, 1)
         self.dt64 = np.datetime64("2011-01-01 09:00Z")
 
-    def time_apply(self, offset):
-        offset.apply(self.date)
-
-    def time_apply_np_dt64(self, offset):
-        offset.apply(self.dt64)
+    def time_add_np_dt64(self, offset):
+        offset + self.dt64
 
     def time_add(self, offset):
         self.date + offset