fix build when compiling with Werror

Compilation was failing on clang16 when compiling with Werror, specifically Wreorder-ctor, this makes sense because of initilization rules in C++, where the order of intialization matters.

m_thread_thread_start_callback & m_thread_terminated_callback are now initialized at the end of the initialization chain in timer_queue's constructor in accordance with the declaration of the header file.