support monotonic functions as sentinels

support monotonic functions as sentinels

Added support for monotonic server-side functions such as PostgreSQL 18's
``uuidv7()`` to work with the :ref:`engine_insertmanyvalues` feature.
By passing ``monotonic=True`` to any :class:`.Function`, the function can
be used as a sentinel for tracking row order in batched INSERT operations
with RETURNING, allowing the ORM and Core to efficiently batch INSERT
statements while maintaining deterministic row ordering.

Fixes: #13014
Change-Id: I2fabf96c8fbdb6c1d255fd4781cbd31fed17e1e9