Re-add <mutex> to HttpClient_WinInet for a self-contained header

The header uses std::recursive_mutex directly, so it should include <mutex>
rather than rely on it being pulled in transitively via pal/PAL.hpp. This keeps
the header self-contained (include-what-you-use) alongside <condition_variable>
for the condition_variable_any member.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bmehta001

lib/http/HttpClient_WinInet.hpp

@@ -13,6 +13,7 @@
 #include "ILogManager.hpp"
 
 #include <condition_variable>
+#include <mutex>
 
 namespace MAT_NS_BEGIN {