erlang: erlang:send_after/3 + cancel_timer/1 + monotonic_time (T1+T2, 766/766)

Logical-clock timer wheel in the scheduler. send_after schedules a
message-delivery event at an absolute deadline (clock + Time ms);
cancel_timer marks a live timer cancelled and reports remaining ms,
or false. Time advances only when the runnable queue drains, jumping
to the earliest pending deadline (deterministic, no wall clock).

monotonic_time/0,1 exposes the logical ms clock.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/erlang/scoreboard.md

@@ -1,6 +1,6 @@
 # Erlang-on-SX Scoreboard
 
-**Total: 761 / 761 tests passing**
+**Total: 766 / 766 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -15,6 +15,7 @@
 | ✅ | fib | 8 | 8 |
 | ✅ | ffi | 37 | 37 |
 | ✅ | vm | 78 | 78 |
+| ✅ | send_after | 5 | 5 |
 
 
 Generated by `lib/erlang/conformance.sh`.