DuckDB window-frame helpers for Ecto queries.

Ecto versions before the release containing ecto#4730 only accept literal fragment(...) calls in a window :frame option. These helpers are ready for that Ecto release; until your project depends on it, use the generated SQL shape directly:

frame: fragment("ROWS BETWEEN 6 PRECEDING AND CURRENT ROW")

Once macro-expanded frames are available in your Ecto version, helpers can be used as:

frame: rows_between({:preceding, 6}, :current_row)
frame: range_between(:unbounded_preceding, {:following, 1})