fix: replace usleep with nanosleep and fix const correctness

Co-authored-by: aider (deepseek/deepseek-reasoner) <aider@aider.chat>

src/main.c

@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <time.h>
 
 int main(int argc, char *argv[]) {
   (void)argc;
@@ -41,7 +42,7 @@ int main(int argc, char *argv[]) {
 
   while (1) {
     looper_process_commands(client);
-    usleep(50000); /* check commands every 50 ms */
+    { struct timespec ts = { .tv_sec = 0, .tv_nsec = 50000000 }; nanosleep(&ts, NULL); } /* check commands every 50 ms */
   }
 
   jack_client_close(client);