This PR begins to parallelize the (presumably) computationally most expensive step: parsing source files. It does so by introducing a worker pool, which the main thread delegates to. Summarized changes:

• Wrapped makeCacheItemFromFilePath with a thread worker pool via piscina.
• Rewrote signature of makeCacheItemFromFilePath to make input/result serializable.
• (style) Introduced prettier plugin to eslint. Arguably, this doesn't need to be part of this PR 🤔

This PR is considered WIP, with some things left to do:

Mandatory:

• Serialize/deserialize user-supplied plugins. Currently, if plugins are configured, every thread will panic, as plugins can't be loaded.
• Serialize/deserialize failures caused in the thread, specifically, anything that is nested in unknown errors (explicit errors should already be handled).
• Optimize. We're only getting ("on my machine") a ~2x speedup compared to single-threaded. Might be related to my machine, but there's probably much more we can get here. Maybe related to the overhead of serialization? Playing around with thread-pool size or queue size might be profitable as well.

Optional:

• Generalize worker pool code. Right now, the code is very specific to makeCacheItemFromFilePath.
• Improve otel tracing in thread. Currently, it's starting an entirely separate trace.