Feat(embeddings): add embedding distance calculator module

[marieaurore123]

• Creates new module in rig::embeddings::distance which defines the trait VectorDistance. The trait allows for dot, cosine, euclidean, manhattan, angular, and chebyshev distances to be calculated between 2 embedding vectors.
• The distance calculations use the par_iter function from the crate rayon to parallelize the calculations. Since rayon is a large crate, the distance module is hidden behind the feature: embedding-distance.
• Changed the cosine similarity equation