[IMP] api, models: _write performances on import

Followup from the previous commit: before this, _write takes 32% of
total runtime, of which 13.7% is ultimately assignable to add_todo.

Turns out for the test case we mostly keep adding records to recorsets
where they're already present, so the 13.7% of runtime in add_todo are
mostly spent creating orderedsets (11.17) then converting those back
into recordsets (1.75%) with some time spent creating lists and
appending records (already present) in them.

Checking if the records are already present before merging them in
decreases add_todo's runtime cost to 0.5%, and ultimately _write to
20%.

As many of the ignorable calls were merging a singleton or an empty
recorset into the parent recordset, optimising for these cases was
added to BaseModel's <= and >=.

odoo/api.py

@@ -955,7 +955,11 @@ class Environment(Mapping):
         recs_list = self.all.todo.setdefault(field, [])
         for i, recs in enumerate(recs_list):
             if recs.env == records.env:
-                recs_list[i] |= records
+                # only add records if not already in the recordset, much much
+                # cheaper in case recs is big and records is a singleton
+                # already present
+                if not records <= recs:
+                    recs_list[i] |= records
                 break
         else:
             recs_list.append(records)

odoo/models.py

@@ -4963,6 +4963,11 @@ class BaseModel(MetaModel('DummyModel', (object,), {'_register': False})):
     def __le__(self, other):
         if not isinstance(other, BaseModel) or self._name != other._name:
             raise TypeError("Mixing apples and oranges: %s <= %s" % (self, other))
+        # these are much cheaper checks than a proper subset check, so
+        # optimise for checking if a null or singleton are subsets of a
+        # recordset
+        if not self or self in other:
+            return True
         return set(self._ids) <= set(other._ids)
 
     def __gt__(self, other):
@@ -4973,6 +4978,8 @@ class BaseModel(MetaModel('DummyModel', (object,), {'_register': False})):
     def __ge__(self, other):
         if not isinstance(other, BaseModel) or self._name != other._name:
             raise TypeError("Mixing apples and oranges: %s >= %s" % (self, other))
+        if not other or other in self:
+            return True
         return set(self._ids) >= set(other._ids)
 
     def __int__(self):