use spdlog for logging in ws + unittest + remove un-needed mutex

third_party/spdlog/include/spdlog/formatter.h

@@ -0,0 +1,20 @@
+//
+// Copyright(c) 2015 Gabi Melman.
+// Distributed under the MIT License (http://opensource.org/licenses/MIT)
+//
+
+#pragma once
+
+#include "fmt/fmt.h"
+#include "spdlog/details/log_msg.h"
+
+namespace spdlog {
+
+class formatter
+{
+public:
+    virtual ~formatter() = default;
+    virtual void format(const details::log_msg &msg, fmt::memory_buffer &dest) = 0;
+    virtual std::unique_ptr<formatter> clone() const = 0;
+};
+} // namespace spdlog