Reworks the worker pool to be more configurable

[arcanis]

What's the problem this PR addresses?

This PR extends @anuragkalia's work in #5636 (it starts from the same commits and builds upon them).

• The original implementation was keeping a singleton worker pool - I felt this was problematic since we may enter situations (even if only in tests) where multiple calls to convertToZip would want to use different pools.

• Converting an archive without using a worker was only possible when the concurrency was completely disabled. This was my idea, but retrospectively it felt better to me to have two settings: one for the concurrency, and another to define whether the concurrency is enabled or not.

• Passing all those settings from the various fetchers would have been unwieldly.

How did you fix it?

• I created a TaskPool interface; WorkerPool implements it (using workers, same implementation as before), but so does AsyncPool (a new implementation that simply forwards the call to the pLimit limiter).

  • I feel like this also addresses @merceyz's comment regarding the setting name - it's now called taskPoolConcurrency, which doesn't directly refers to workers.

• A getConfigurationWorker function returns the proper task pool for the given configuration object. To make that possible, WeakMap instances can now be used as storage argument for the get*WithDefault family of functions.

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.