dotbot/simulator: various improvements

[aabadie]

Summary

• More accurate robot geometry: updated wheel diameter (D) from 50 mm to 44 mm and wheelbase (L) from 70 mm to 78 mm to better match the physical hardware
• Removed PWM dead-zone clamp: eliminated MIN_PWM_TO_MOVE threshold so small PWM values are no longer clamped to zero, giving smoother low-speed simulation
• Adjusted angular speed gain: tuned ANGULAR_SPEED_GAIN from 2 to 1.5 for better Python control-loop tracking
• Consistent simulation timestep: changed SIMULATOR_STEP_DELTA_T from 20 ms to 50 ms to match the real firmware control loop period
• Removed unused constant: dropped DIRECTION_THRESHOLD which was no longer referenced
• Improved CMakeLists for utils/control_loop: converted DOTBOT_VERSION to a CMake cache variable and added two new cache options (BUILD_WITH_EKF, BUILD_WITH_PURE_PURSUIT) to conditionally enable EKF and Pure Pursuit support via compile-time definitions
• Updated README: expanded build instructions with a CMake options table, examples for enabling optional features, and ccmake TUI usage
• Updated .gitignore: broaden pattern from build/ to build*/ to ignore all build directory variants