Clean __osMalloc.c (#4351)

* Remove #ifs

* Add `NODE_IS_VALID`

* Fix current macros

* `NODE_GET_NEXT` & `NODE_GET_PREV`

* Add macros

* Use macros and general cleanup

* Fix build (hopefully)

* Address review

soh/src/code/debug_malloc.c

@@ -109,5 +109,5 @@ void DebugArena_Cleanup(void) {
 }
 
 u8 DebugArena_IsInitalized(void) {
-    return __osMallocIsInitalized(&sDebugArena);
+    return __osMallocIsInitialized(&sDebugArena);
 }