Fixes needed to enable compilation with gcc 13 (#96)

include/signalrclient/signalr_value.h

@@ -9,6 +9,7 @@
 #include <vector>
 #include <map>
 #include <cstddef>
+#include <cstdint>
 
 namespace signalr
 {

src/signalrclient/cancellation_token_source.h

@@ -8,6 +8,8 @@
 #include <condition_variable>
 #include <mutex>
 #include <vector>
+#include <string>
+
 #include "signalrclient/cancellation_token.h"
 
 namespace signalr