bio: add bioShutdown function to prevent memory leaks

This commit implements the bioShutdown() function, which guarantees
a graceful shutdown of the background I/O subsystem. It destroys
worker mutexes, condition variables, releases job lists, and closes
the event loop synchronization pipes.

This ensures no resource leaks are left behind upon server exit.

bio.c

@@ -12,6 +12,7 @@
  * we'll switch to libeio. However there are probably long term uses for this
  * file as we may want to put Redis specific background tasks here.
  *
+ *
  * DESIGN
  * ------
  *
@@ -54,6 +55,7 @@ static char* bio_worker_title[] = {
     "bio_lazy_free",
 };
 
+
 #define BIO_WORKER_NUM (sizeof(bio_worker_title) / sizeof(*bio_worker_title))
 
 static unsigned int bio_job_to_worker[] = {