- UPDATE statements can now be batched within an ORM flush

- UPDATE statements can now be batched within an ORM flush
into more performant executemany() call, similarly to how INSERT
statements can be batched; this will be invoked within flush
to the degree that subsequent UPDATE statements for the
same mapping and table involve the identical columns within the
VALUES clause, as well as that no VALUES-level SQL expressions
are embedded.
- some other inlinings within persistence.py