Do ORMs provide interfaces for working with window functions?
Not really.

While some ORMs may very well be able to utilize windowing functions you yourself write none of them will be able to generate window functions. ORMs map data to data. They are an Object Oriented to relational data-translation layer. Window functions are a data-processing feature. It's a declarative way to process a result set, they run in the last-step of result-set generation, docs:


  If the query contains any window functions, these functions are evaluated after any grouping, aggregation, and HAVING filtering is performed. That is, if the query uses any aggregates, GROUP BY, or HAVING, then the rows seen by the window functions are the group rows instead of the original table rows from FROM/WHERE.


At the point a Window Function works, the authors of an ORM may as well map the syntax into their own result-set processing features.