feat(causal): wall-anchored timers — controller windows keep fixed wall length (RFC 007)

New timer anchor: insert_sleep_wall / scheduler::sleep_wall (exported) opt a
Sleep entry out of the RFC 007 virtual-time shift, so it fires at its raw
deadline regardless of injected delay. Featureless config is unchanged (the
API exists but is identical to sleep).

The causal controller's window/cooldown sleeps and the tsc_hz calibration
sleep use it on the actor path (the OS-thread path was already wall). This
fixes the controller's own sleeps dilating under its own injection —
experiment windows stretched ~2x at 50% speedup (337ms -> 646ms injected/
window). Deltas were rate-normalized so results were unbiased; this fixes
sweep cost, not bias. The general wall-anchored-timer-semantics jar item
(user-facing opt-out) remains open; this lands the substrate.

Test: wall_timer_ignores_injected_delay — wall entry fires at raw deadline
while a virtual sibling in the same heap shifts. 13/13 causal, 34/34
binaries both feature configs.

src/scheduler.rs

@@ -403,6 +403,28 @@ pub fn sleep(duration: std::time::Duration) {
     park_current();
 }
 
+/// Like [`sleep`], but wall-anchored: under causal profiling (feature
+/// `smarm-causal`) the deadline is honoured in wall time instead of chasing
+/// injected virtual delay. Identical to [`sleep`] without the feature. For
+/// measurement machinery whose durations define wall time (the causal
+/// controller's windows, TSC calibration) — workload code wants [`sleep`].
+pub fn sleep_wall(duration: std::time::Duration) {
+    let me = match current_pid() {
+        Some(pid) => pid,
+        None => panic!("sleep_wall() called outside an actor"),
+    };
+    let _np = NoPreempt::enter();
+    let epoch = begin_wait();
+    let deadline = crate::timer::deadline_from_now(duration);
+    with_runtime(|inner| {
+        match inner.timers.lock() {
+            Ok(mut timers) => timers.insert_sleep_wall(deadline, me, epoch),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
+    });
+    park_current();
+}
+
 pub fn insert_wait_timer(
     deadline: std::time::Instant,
     pid: Pid,