Add dataset converter tools for standard research datasets

[jbrodovsky]

Free Core Feature

The Free Core spec requires tools to import third-party datasets (KITTI, nuScenes, Carla, MEMS-Nav) into the required format for strapdown-sim.

Requirements:

• CLI tool or interactive converter for each supported dataset format:
  • KITTI (autonomous driving dataset)
  • nuScenes (autonomous driving dataset)
  • Carla (simulation environment)
  • MEMS-Nav (existing MEMS IMU datasets)
• Output in standardized CSV format compatible with strapdown-sim
• Validation of converted data
• Documentation for each converter with examples

Acceptance Criteria:

• User can convert datasets: strapdown-convert --format kitti --input data/ --output converted.csv
• Converters handle missing fields gracefully
• Output CSV passes validation for strapdown-sim
• README documents conversion process for each format