Add SpatialLeiden as clustering method

Basically already (mostly) uses `scanpy` / `squidpy` for preproc steps, could wrap remaining python code and provide as method: 
![image](https://github.com/user-attachments/assets/aa62f6bc-6407-4e2a-804b-71f11e6d6d0e)


https://www.biorxiv.org/content/10.1101/2024.08.23.609349v1