To allow parallelizing neume strategy transformations, refactor extraction worker

[TimDaub]

Scope

• Not only do we have to parallelize neume extraction, but also transformation
• Currently, the strategy lifecycle repository hard codes running all transformers in sequence, e.g. here: https://github.com/neume-network/strategies/blob/9a5d75c7b2535998ddf5be562f8466e2b99de68e/src/lifecycle.mjs#L49
• In the future, we want to be able to use multiple parallel processes to transform flat files; for that it'd be useful if the "extraction-worker" was a general-purpose worker, e.g., if it was able to also handle transformations

Dependent on

• More architectural work is required to do this issue.