Add typed window function builders with OVER clauses

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What this task asks for

Add typed query-builder helpers for SQL window functions, named windows, and frame specs. Add typed ranking, offset, value, and aggregate window helpers whose builders expose `.over()`. Support inline and named window specifications with partitioning, ordering, and row or range frames. Emit numeric positional arguments as SQL literals rather than bound parameters. Validate positional arguments, window names, frame ordering, and frame-boundary offsets. Compile named windows before `ORDER BY` and named references as quoted `OVER` names without parentheses. Export all helpers and preserve nullable value-access typing, removing null when lag or lead has a default.