feat: add opt-in twoslash build cache

[IMax153]

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The changes in this PR will be included in the next version bump.

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Name	Type
expressive-code-twoslash	Patch

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[IMax153]

👋 Hey @Adammatthiesen! We're currently working on the next iteration of the Effect Website, and I'm trying to optimize build times as much as possible.

As you know, we make heavy use of your expressive-code-twoslash plugin for rendering our code snippets, and I'm sure you know that the more Twoslash snippets you have, the slower the build times.

I've been experimenting on our new site with a build-time cache for Twoslash snippets. I locally patched the expressive-code-twoslash plugin to include support for caching Twoslash snippets based on deterministic keys.

For an Astro build with my cache PoC including ~40 Twoslash snippets, the cold build time was ~25s and warm build time was ~15s. Obviously this scales with more and more snippets that are cached vs. uncached, and the actual Effect website has many more snippets than this.

Given the positive results, I figured I'd make a PR to expressive-code-twoslash to see if you're interested in upstreaming this functionality.

Please note that the PR is fully AI generated - I'm happy to clean it up if you're interested in upstreaming it, and also happy to make whatever changes to the public API you want too!