core: rewrite panic sites as explicit match+panic

Replace implicit unwrap()/expect() in the lock-ordered core with explicit
match arms. Lock-poison sites use one uniform message
("smarm: <lock> lock poisoned (core corrupt): {e}"); invariant sites panic
with a descriptive message naming the violated invariant. No behaviour
change: each rewrite preserves the prior panic-on-bad-arm semantics. Also
clears the accompanying clippy hygiene in these files (redundant_closure,
len_without_is_empty, too_many_arguments, unnecessary_sort_by,
missing_safety_doc, nonminimal_bool/unnecessary_unwrap).

src/context.rs

@@ -94,10 +94,28 @@ unsafe extern "C" fn switch_to_actor_asm() {
 }
 
 /// Resume the actor whose sp is in `ACTOR_SP`. Returns when the actor yields.
+///
+/// # Safety
+///
+/// The caller must be running on a scheduler thread with a valid actor stack
+/// pointer installed in `ACTOR_SP` — either by `init_actor_stack` (first
+/// resume) or by a prior `switch_to_scheduler` (subsequent resumes). Resuming
+/// with an unset or stale `ACTOR_SP` transfers control to an arbitrary address.
+/// Must not be called from within an actor (only the scheduler side may resume).
 pub unsafe fn switch_to_actor() {
     unsafe { switch_to_actor_asm() };
 }
 
+/// Yield from the running actor back to its scheduler thread. Returns when the
+/// actor is next resumed via [`switch_to_actor`].
+///
+/// # Safety
+///
+/// The caller must be running on an actor stack that was entered through
+/// [`switch_to_actor`], so that `SCHEDULER_SP` holds the live saved stack
+/// pointer of the scheduler side. Calling this from the scheduler thread, or
+/// before any actor has been resumed, transfers control to an arbitrary
+/// address.
 #[unsafe(naked)]
 pub unsafe extern "C" fn switch_to_scheduler() {
     core::arch::naked_asm!(