fix: wrap windowed aggregates (swev-id: django__django-17084)

[casey-brooks]

Summary

• detect when aggregates reference window annotations and force subquery wrapping
• add regression coverage ensuring the ORM emits a wrapped query for window aggregates
• confirm aggregation over window annotations now succeeds on backends with OVER support

Observed failure

psycopg2.errors.GroupingError: aggregate function calls cannot contain window function calls

Stack trace

psycopg2.errors.GroupingError: aggregate function calls cannot contain window function calls
  File "django/db/backends/utils.py", line XXX, in _execute
    return self.cursor.execute(sql, params)
  File "django/db/models/sql/compiler.py", line XXX, in execute_sql
    cursor.execute(sql, params)
  File "django/db/models/query.py", line XXX, in aggregate
    return query.chain().get_aggregation(self.db, kwargs)
  ...

Reproduction steps

1. Annotate a queryset with a window expression, e.g. Window(Sum("value"), order_by=F("date").asc()).
2. Aggregate over both the original value and the window annotation.
3. Run the query on PostgreSQL.
4. Observe Django emits SUM(Window(...)) in a single SELECT and PostgreSQL raises psycopg2.errors.GroupingError.

Fix

• track whether aggregates reference annotations whose expressions contain an OVER clause during resolution
• include this flag when deciding whether to wrap the base query in an aggregate subquery
• add a regression test confirming the ORM generates a subquery and the aggregate succeeds

Testing

• PYTHONPATH=$PWD:$PWD/tests:$HOME/.nix-profile/lib/python3.11/site-packages DJANGO_SETTINGS_MODULE=tests.test_sqlite $HOME/.nix-profile/bin/python3.11 tests/runtests.py aggregation --parallel=1
• $HOME/.nix-profile/bin/python3.11 -m flake8 django/db/models/sql/query.py tests/aggregation/tests.py

Fixes #537

[casey-brooks]

Tests & Lint Summary:

• PYTHONPATH=/workspace/django:/workspace/django/tests:/root/.nix-profile/lib/python3.11/site-packages DJANGO_SETTINGS_MODULE=tests.test_sqlite /root/.nix-profile/bin/python3.11 tests/runtests.py aggregation --parallel=1 → 125 passed, 0 failed, 0 skipped
• /root/.nix-profile/bin/python3.11 -m flake8 django/db/models/sql/query.py tests/aggregation/tests.py → no lint issues

[noa-lucent]

LGTM. Verified subquery wrapping for aggregates on window annotations and the new test covers the regression.

[rowan-stein]

Validated locally:

• Checked out branch noa/issue-537.
• Ran tests for aggregation module (tests/aggregation/tests.py) using a Python 3.12 venv.
• All 108 aggregation tests passed.
• The new test AggregateTestCase.test_aggregate_over_window_annotation passes and confirms subquery wrapping when aggregating over window annotations.
  No further changes required.