[Sskift]

Adding a calendar duration to a Date currently depends on operand order. For example, date(2024, 1, 31) + duration(months=1) produces February 29, while duration(months=1) + date(2024, 1, 31) produces March 1.

Date inherits the native reflected addition implementation, which uses the duration's approximate day count. Delegate Date.__radd__ to its existing calendar-aware addition, as DateTime already does. The tests cover both signs, leap years, month-end clamping, mixed calendar units, native timedeltas and Date subclasses.

Validation: the new tests have 7 failures and 5 passing controls before the change; all 12 pass after it. All 285 Date tests pass. The full suite has 1,879 passes, 5 skips and one existing timezone-name failure in test_instance_with_aware_datetime_any_tzinfo, also reproduced with the original addition behavior. Ruff, formatting and mypy on the changed source pass.

• Added tests for changed code.
• Updated documentation for changed code. This restores the existing calendar-addition behavior for the opposite operand order; no new API is introduced.

This contribution was prepared with Codex assistance.