feat: add onUsr1, streq and printOut

user/spawntarget.c

@@ -0,0 +1,13 @@
+#include "ulib.h"
+
+/* A plain child program: only ever launched via proctest.c's userSpawn, so
+   its pid is a genuinely different, freshly created thread rather than the
+   caller's own (unlike exectarget.c, which replaces the caller in place). */
+
+int main(void)
+{
+    print("spawntarget: child running, pid=");
+    printDec(userGetpid());
+    print("\n");
+    return 3;
+}