CppServer::Asio::Timer is not thread-safe

[herolover]

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CppServer::Asio::Timer::Cancel method must be called from its io_context, otherwise there is a data race.

https://www.boost.org/doc/libs/1_75_0/doc/html/boost_asio/reference/system_timer.html#boost_asio.reference.system_timer.thread_safety

Or mark CppServer::Asio::Timer as not thread-safe.

P.S. I highly recommend to test all of your libs with thread sanitizer.