feat: add RadialFourier3D and RadialFourierFeatures3D transforms

- Implement 3D radial Fourier transform for rotation-invariant frequency analysis
- Support radial binning, magnitude/phase output, normalization, and exact inverse
- Add RadialFourierFeatures3D for multi-scale feature extraction
- Add comprehensive unit tests (20 tests covering shapes, inverse, batch, numpy, etc.)
- Fix test discovery and mypy compatibility

Author: Hitendrasinhdata7