-- tz-offset tz:t epoch:n > R n t
-- Returns the UTC offset in seconds for a named IANA timezone at a
-- given Unix epoch. Positive = east of UTC. DST-aware via chrono-tz.
-- Returns Err on unknown timezone name.
-- London in winter (GMT, UTC+0): 2024-01-01 12:00:00 UTC
london-winter-offset n:n>R n t;tz-offset "Europe/London" n
-- London in summer (BST, UTC+1 = 3600s): 2024-07-01 12:00:00 UTC
london-summer-offset n:n>R n t;tz-offset "Europe/London" n
-- Tokyo (JST, UTC+9 = 32400s, no DST): any epoch
tokyo-offset n:n>R n t;tz-offset "Asia/Tokyo" n
-- New York in winter (EST, UTC-5 = -18000s): 2024-01-15 12:00:00 UTC
nyc-winter-offset n:n>R n t;tz-offset "America/New_York" n
-- New York in summer (EDT, UTC-4 = -14400s): 2024-07-15 12:00:00 UTC
nyc-summer-offset n:n>R n t;tz-offset "America/New_York" n
-- run: london-winter-offset 1704110400
-- out: 0
-- run: london-summer-offset 1719835200
-- out: 3600
-- run: tokyo-offset 0
-- out: 32400
-- run: nyc-winter-offset 1705320000
-- out: -18000
-- run: nyc-summer-offset 1721044800
-- out: -14400