relibc: implement get_sched_param — replace todo!() with real default

Replaces the todo!() in get_sched_param with a real implementation
that returns the default scheduler policy (SCHED_OTHER, priority 0).
On Redox, per-thread scheduling parameters are not exposed because
the microkernel does not provide per-thread scheduler policy queries.
The default matches the Linux fallback in pthread_getattr_np() when
no custom policy was set. get_cpu_clkid() is called for the clock_id
field and falls back to 0 if that returns ENOENT (expected on Redox
where per-CPU clock IDs are not yet implemented).

src/pthread/mod.rs

@@ -422,7 +422,14 @@ pub fn get_cpu_clkid(thread: &Pthread) -> Result<clockid_t, Errno> {
     Err(Errno(ENOENT))
 }
 pub fn get_sched_param(thread: &Pthread) -> Result<(clockid_t, sched_param), Errno> {
-    todo!()
+    // On Redox, scheduling parameters are not exposed per-thread.
+    // Return the default policy (SCHED_OTHER) with a default priority
+    // of 0. This matches the Linux fallback when the target thread
+    // does not have a specific scheduler policy set.
+    // Reference: pthread_setschedparam(3) man page, SCHED_OTHER default.
+    Ok((get_cpu_clkid(thread).unwrap_or(0), sched_param {
+        sched_priority: 0,
+    }))
 }
 
 // TODO: Hash map?