OptiTrack on ROS2 Humble: prevent NatNet ABI link failures, fix model-def segfault

[Lorite]

• Problem:
  • Ubuntu 22.04 / ROS2 Humble users can hit linker failures when closed-source NatNet binaries require newer GLIBC/GLIBCXX.
  • Runtime segfault occurred in OptiTrack model definition parsing with malformed/newer packet layouts.
• Fix summary:
  • Force closed-source OptiTrack backend OFF in parent CMake cache; install libNatNet only when that backend is enabled.
  • Harden parseModelDef with bounds checks and safe string consumption.
  • Make interface binding configurable with interface_ip fallback to 0.0.0.0.
  • Keep dependency scope minimal: include NatNetSDKCrossplatform bump only (no vrpn/vicon bump).
• Validation:
  • colcon build --symlink-install --packages-select motion_capture_tracking passed.
  • Runtime no longer segfaults at startup with type:=optitrack.
• PR:
  • Will be opened from Lorite/motion_capture_tracking:ros2 to IMRCLab/motion_capture_tracking:ros2.