Allow out-of-crate preprocessed column definitions

[yoichi-nexus]

This PR removes an enum PreprocessedColumn and introduces a trait PreprocessedColumnOps. The enum values are turned into trait implementations.

Motivation

Before this PR, when a stwo user wanted a new column in the preprocessed column, they had to change stwo codebase and add a value in PreprocessedColumn enum.

After this PR, they can implement PreprocessedColumnOps in their own crate, without touching stwo codebase.

[reviewable-StarkWare]

This change is 

[yoichi-nexus]

I got early feedbacks. I want to give it another try

• I'll keep the new trait as is
• I'll add type PreprocessedColumn: Preprocessed ColumnOps in the EvalAtRow interface

This would eliminate the dynamic dispatch business, and will be a straightforward generalization of the current codebase.

[yoichi-nexus]

I'll add type PreprocessedColumn: Preprocessed ColumnOps

Didn't quite work out. I am adding tons of type arguments everywhere. At the moment this PR is still my best try.