v9.1.0

• Switch tr Ramazan and Kurban Bayramı to a calculated Hijri date instead of a hand-maintained per-year table, so they no longer silently disappear past 2030. definitions pull-385, definitions issue-377
• Fix vn Giỗ tổ Hùng Vương test dates for 2018-2023; the 2018 date was wrong due to a lunar calendar leap-month bug. definitions pull-386, definitions issue-150
• Shift observed us Independence Day off weekends for every region via a new independence_day function, replacing the us_va-only to_weekday_if_weekend shim; nearest weekday for most regions, the following Monday for us_ri, no shift for us_tx. definitions pull-387, holidays issue-478