Add transformer option

[hmbrg]

This implements #46.

This allows passing a transformer library like superjson to serialize data types that are not supported by JSON.stringify.
The API for this option was inspired by https://trpc.io/docs/data-transformers#using-superjson.

You can use a transformer like this on a per-cache basis:

import superjson from "superjson"

const cache = new Cache({
  storage: createStorage(),
  transformer: superjson
})

Alternatively, a transformer can be added for a specific function:

import superjson from "superjson"

cache.define('fetchSomething', {
  transformer: superjson
}, async (query, cacheKey) => {
  return { k: query }
})

I've tried creating tests for this, but the test are failing without any error message.
Since I'm not too familiar with tap for testing, I was hoping somebody could look into this.

I hope this is helpful!

[mcollina]

I think the test is good but there was a bug in your implementation.

[mcollina]

Suggested change

	return this.transformer.deserialize(this.storage.get(key))
	return this.transformer.deserialize(await this.storage.get(key))

[hmbrg]

Good catch, thanks! I changed this, but sadly the error remains. I've also added documentation and an example to the README.

[hmbrg]

Okay, I've managed to fix all the errors. There actually was another bug in the implementation.

[mcollina]

lgtm

[mcollina]

Apparently the code coverage is too low: https://github.com/mcollina/async-cache-dedupe/actions/runs/4162364135/jobs/7203097232#step:6:1656

[hmbrg]

Apparently the code coverage is too low: https://github.com/mcollina/async-cache-dedupe/actions/runs/4162364135/jobs/7203097232#step:6:1656

Fixed it!

[mcollina]

lgtm