fix: add eventfd_t typedef in trailer for cbindgen

src/header/sys_eventfd/cbindgen.toml

@@ -1,6 +1,8 @@
 sys_includes = ["stdint.h", "stddef.h"]
 include_guard = "_SYS_EVENTFD_H"
 trailer = """
+typedef uint64_t eventfd_t;
+
 int eventfd(unsigned int initval, int flags);
 int eventfd_read(int fd, eventfd_t *value);
 int eventfd_write(int fd, eventfd_t value);