erlang: send_after deadline-ordering + cancel-of-fired tests (T3+T4, 769/769)

T3 — concurrent timers fire in deadline order, not schedule order
(scheduler jumps the clock to the earliest pending deadline each
time the runnable queue drains). T4 — cancel_timer on an
already-fired timer returns the atom false.

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: 766 / 766 tests passing**
+**Total: 769 / 769 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -15,7 +15,7 @@
 | ✅ | fib | 8 | 8 |
 | ✅ | ffi | 37 | 37 |
 | ✅ | vm | 78 | 78 |
-| ✅ | send_after | 5 | 5 |
+| ✅ | send_after | 8 | 8 |
 
 
 Generated by `lib/erlang/conformance.sh`.