Investigate if code can be simplified by using factor_contrasts

[grst]

Description of feature

In formulaic 1.1, a new property factor_contrasts has been introduced that allows to introspect some properties of factors. This should allow us to simplify our custom materializer and in the best case get rid of it entirely.

See

matthewwardrop/formulaic#169 (comment)

and

https://github.com/matthewwardrop/formulaic/blob/28fd9ec2d66b0f4c3fab439445e2e3a78174e9ca/formulaic/model_spec.py#L334-L361