fix: Add missing include when building with boost 1.91

[soerengrunewald]

Why

When build with boost 1.91 the compiler complains:

In file included from DeviceAccess/backends/Rebot/src/Connection.cc:4:
DeviceAccess/backends/Rebot/src/Connection.h:45:18: error: ‘deadline_timer’ in namespace ‘boost::asio’ does not name a type
   45 |     boost::asio::deadline_timer disconnectTimer_;
      |                  ^~~~~~~~~~~~~~
DeviceAccess/backends/Rebot/src/Connection.h:46:18: error: ‘deadline_timer’ in namespace ‘boost::asio’ does not name a type
   46 |     boost::asio::deadline_timer::duration_type connectionTimeout_;
      |                  ^~~~~~~~~~~~~~
DeviceAccess/backends/Rebot/src/Connection.cc: In constructor ‘ChimeraTK::Rebot::Connection::Connection(std::string, std::string, uint32_t)’:
DeviceAccess/backends/Rebot/src/Connection.cc:14:75: error: class ‘ChimeraTK::Rebot::Connection’ does not have any field named ‘disconnectTimer_’
   14 |   : address_(std::move(address)), port_(std::move(port)), s_(ioContext_), disconnectTimer_(ioContext_),
      |                                                                           ^~~~~~~~~~~~~~~~
DeviceAccess/backends/Rebot/src/Connection.cc:15:5: error: class ‘ChimeraTK::Rebot::Connection’ does not have any field named ‘connectionTimeout_’
   15 |     connectionTimeout_(boost::posix_time::seconds(connectionTimeout_sec)) {}
      |     ^~~~~~~~~~~~~~~~~~
DeviceAccess/backends/Rebot/src/Connection.cc:15:43: error: ‘seconds’ is not a member of ‘boost::posix_time’
   15 |     connectionTimeout_(boost::posix_time::seconds(connectionTimeout_sec)) {}
      |                                           ^~~~~~~

How

Add the missing include, though this will solve the problem only partially, as it will compile, but emit warnings, as the deadline timer is marked deprecated and should be replaced with system_timer.