Image fps improvement

[jonyMarino]

This pull request introduces several improvements and fixes across both the Python client and the C++ core simulation components, focusing on more robust connection management, improved serialization performance, and enhanced topic handling. The changes include the addition of a service-only connection mode for the Python client, optimizations to image message serialization in C++, and more reliable and thread-safe topic connection tracking in the core simulator.

Python client enhancements:

• Added a connect_services method to ProjectAirSimClient to allow connecting only to the service socket, which is useful when another process owns the topic socket (e.g., for ROS bridge integration). (client/python/projectairsim/src/projectairsim/client.py)
• Improved socket timeout handling and minor code simplifications, such as direct returns and thread-safe disconnect logic. (client/python/projectairsim/src/projectairsim/client.py) [1] [2] [3] [4]
• Added StaticSensorActor to the public API. (client/python/projectairsim/src/projectairsim/__init__.py)

C++ core simulation improvements:

• Optimized ImageMessage serialization by replacing std::stringstream with a custom buffer, reducing allocations and improving efficiency. (core_sim/src/message/image_message.cpp) [1] [2]
• Refactored and improved topic frame packing, introducing utility writers for efficient and safe message construction. (core_sim/src/topic_manager.cpp)
• Added robust, thread-safe tracking of active topic pipes to ensure correct handling of client connect/disconnect events and subscription resets only when all pipes are closed. (core_sim/src/topic_manager.cpp) [1] [2] [3] [4] [5] [6]
• Minor improvements to logging, error handling, and code style in topic subscription and unsubscription logic. (core_sim/src/topic_manager.cpp) [1] [2] [3]

Build and dependency cleanups:

• Fixed include order and removed redundant includes in C++ files and CMake configuration. (core_sim/src/CMakeLists.txt, client/cpp/ProjectAirsimClientLib/src/Topics.h, core_sim/src/message/image_message.cpp, core_sim/src/sensors/camera.cpp) [1] [2] [3] [4]

ONNX model post-processing:

• Simplified ONNX execution provider selection logic in the camera sensor code. (core_sim/src/sensors/camera.cpp)

These changes collectively improve the reliability, efficiency, and extensibility of both the client and core simulation components.