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

third_party/spdlog/tests/utils.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <cstddef>
+#include <string>
+
+std::size_t count_lines(const std::string &filename);
+
+void prepare_logdir();
+
+std::string file_contents(const std::string &filename);
+
+std::size_t count_lines(const std::string &filename);
+
+std::size_t get_filesize(const std::string &filename);
+
+bool ends_with(std::string const &value, std::string const &ending);