BUILD: proxy: include tools.h in proxy.c

Many functions are used from tools.h but the file wasn't included and
was inherited through others.
diff --git a/src/proxy.c b/src/proxy.c
index 4423686..ce60df0 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -48,6 +48,7 @@
 #include <haproxy/task.h>
 #include <haproxy/tcpcheck.h>
 #include <haproxy/time.h>
+#include <haproxy/tools.h>
 #include <haproxy/xprt_quic.h>