restructure: move el compiler content into lang/

lang/tests/calendar/examples/cross-calendar-comparison.el

@@ -0,0 +1,22 @@
+// cross-calendar-comparison.el — same Instant under two different calendars
+// produces identical cal_to_instant() outputs. Calendar choice does not change
+// the underlying instant — only the projection.
+
+fn run_test() -> Int {
+    let i: Instant = unix_seconds(1782216000)
+    let z: Zone = zone("America/New_York")
+    let earth: Calendar = earth_calendar(z)
+    let mars: Calendar = mars_calendar()
+    let ct_earth: CalendarTime = in_calendar(i, earth)
+    let ct_mars: CalendarTime = in_calendar(i, mars)
+    let i_earth: Instant = cal_to_instant(ct_earth)
+    let i_mars: Instant = cal_to_instant(ct_mars)
+    if i_earth == i_mars {
+        return 1
+    }
+    return 0
+}
+
+fn main() -> Void {
+    println(int_to_str(run_test()))
+}