feat: add method to unlink storage

[EvanHahn]

This adds MultiCoreIndexer.prototype.unlink() which unlinks all the index storage.

Addresses #26. Depends on #35 because it uses ??=.

[achou11]

first time i'm seeing ??= in app code - took a second to understand that it short-circuits, which makes me have mixed feelings about its existence 😄

Changes look good overall, but had a small question that I'd consider non-blocking

[achou11]

i'm assuming there's an edge case that this accounts for but just in case: would a no-op (or throw) be possible here if the storage isn't initialized? e.g. if (!this.#storage) return

this seems to be performing operations that cancel each other out if the storage isn't already initialized, but maybe it's much more complex than that

[EvanHahn]

There might be cases where the storage has been created on disk but hasn't been initialized in memory. For example:

1. I start the app, index a bunch of stuff, and then close it.
2. Later, I start the app and immediately unlink. this.#storage won't be created. We want to create it so we can unlink it.

My understanding is that creating the storage instance doesn't actually touch any files on disk. For example:

const RandomAccessFile = require("random-access-file")
const fs = require("node:fs")

new RandomAccessFile("my-file.txt")

fs.existsSync("my-file.txt")
// => false

Maybe it's worth adding an explainer comment about this?

[achou11]

ah okay that makes more sense! I was under the impression that this class fully manages the storage on disk but if it's being done somewhere else, your reasoning is clearer. thanks!

[EvanHahn]

I'll plan to merge this tomorrow barring objections. (Feel free to merge sooner if you want!)