feat: use Deno KV for storing fresh assets

[tlgimenes]

This PR adds esbuild assets to Deno KV. This feature uses Deno KV as an optimization and KV is not required for serving assets on both dev and production environments.

How does it work?

All isolate instances have an internal inMemory cache. We use the following algorithm for incoming requests:

if file in in-memory-cache then
  return in-memory-cache[file]
else if file in kv
  return kv[file]
else 
  bundle assets 
  store assets in in-memory-cache
  return in-memory-cache[file]
  store assets in kv in background
  housekeep stale assets in background

With this algorithm, we ensure:

1. Any isolate is able to serve the website without relying on KV.
2. If an asset is inside kv, any isolate is able to return it
3. KV is bounded by housekeeping stale assets

2 is nice because it should remove issues of missing assets when any chunk changes due to esm.sh changes

Consistency

store assets in kv in background means:

1. Files are split into 64Kb chunks and saved in KV in a kv transaction. This ensures the file is stored consistently on KV
2. chunks are stored before islands and entrypoints. This ensures that if an island is served, it's corresponding chunks are retrievable from KV. This ensures no more issues with missing assets when serving the store

Note that KV currently has a limit of 10 operations in a transaction. If your asset is bigger than 10 * 64Kb, it will fail saving on KV, but it's ok since the isolates work without KV

Streaming

A nice approach to saving assets in KV in 64Kb chunks is that we are able to stream these chunks when serving assets from KV

Debug

Since this is a difficult feature to get right, I'm adding a bunch of console.logs that may be removed in the future. To make your life more pleasant, I added emojis! 🎉

I hope to make this PR a fresh PR one day.

[lucis]

Any change that bundleAndCacheOnce will not succeed in putting path in inMemoryCache?

[tlgimenes]

We currently have the same behavior, so I don't think this is an issue