restructure: move el compiler content into lang/

lang/tests/calendar/examples/dst-spring-forward.el

@@ -0,0 +1,17 @@
+// dst-spring-forward.el — Earth calendar handles the DST transition.
+// 2026 spring DST: March 8 at 02:00 EST → clocks jump to 03:00 EDT.
+// 2026-03-08 06:30 UTC = 01:30 EST (just before the jump).
+// Add 1 hour → 07:30 UTC = 03:30 EDT (the wall clock skipped 02:30 entirely).
+
+fn run_test() -> String {
+    let z: Zone = zone("America/New_York")
+    let cal: Calendar = earth_calendar(z)
+    let i: Instant = unix_seconds(1772951400)
+    let later: Instant = i + 1.hour
+    let ct: CalendarTime = in_calendar(later, cal)
+    return cal_format(ct, "HH:mm z")
+}
+
+fn main() -> Void {
+    println(run_test())
+}