I'm struggling getting the affine matrix (or crs_transform) using `pyproj`. The `Transformer`object is full of functions to actually transform coordinates but I just want to check the matrix: 

I'm stucked here : 
```
import pyproj 

toto = pyproj.transformer.Transformer.from_crs("EPSG:3857", "EPSG:4326")
toto.to_json()
```