Feat: per vendor fetch

[marcinpsk]

Summary by CodeRabbit

• New Features

  • Export NetBox device/module/rack types to a local repo via --export-diff.
  • Verify image presence and integrity with --verify-images (HTTP checks + local hash cache).
  • Optionally remove unmanaged component types with --remove-unmanaged-types.
  • Per-vendor processing and vendor-slug fast-paths for faster imports.

• Documentation

  • Expanded CLI docs with usage examples and detailed image verification behavior.

• Bug Fixes / UX

  • Improved progress handling and clearer NetBox connection error messages.

• Tests

  • Expanded test coverage across import/export, image handling, serialization, and safety checks.

• Chores

  • Updated .gitignore to omit local caches and export artifacts.