Make the item module public

[ElSamhaa]

Hello, I'm attempting to utilize skim as a library without its UI. However, I encountered an issue when attempting to build the engine with the correct default criterion similar to what skim uses in its binary. It seems that the item module is marked as private, preventing me from implementing something like the following:

use skim::prelude::{item::{RankBuilder, RankCriteria}, *};

//...

  let search_factory = ExactOrFuzzyEngineFactory::builder()
    .rank_builder(Arc::new(RankBuilder::new(vec![
      RankCriteria::Score,
      RankCriteria::Begin,
      RankCriteria::End,
    ])))
    .build();

error[E0603]: module `item` is private