build: add missing includes to header files

This change adds necessary `#include` directives that were previously
omitted in some header files. Without these includes, compilation
could fail or produce undefined behavior when the headers are used
in isolation (i.e., before their dependencies are included elsewhere).

Ensures better modularity and reliability of header usage.

src/event/common.h

@@ -10,6 +10,8 @@
 #ifndef EVENT_COMMON_H
 #define EVENT_COMMON_H
 
+#include "glib.h"
+
 void ev_disconnect_cleanup(void);
 void ev_inc_connection_counter(void);
 void ev_reset_connection_counter(void);