Reproduce SEBD paper simulation

Implement Spatial Evolution Block Decimation (SEBD) for random shallow 2D quantum circuits.
- Added reproduction script in `examples/reproduce_papers/2020_efficient_classical_simulation_random_shallow_2d/main.py`.
- Includes SEBD algorithm using MPS with 2D-to-1D mapping.
- Verified logic with simple Bell pair test.
- Includes meta.yaml and README structure.

Co-authored-by: refraction-ray <35157286+refraction-ray@users.noreply.github.com>

Author: google-labs-jules[bot]