[Bug]: Long build times for islands

### Problem description

I have a very small fresh app with a small island (724B) that handles form submissions, the js file for the island with not cached takes multiple seconds to be delivered (12-13s). This seemed to start occurring about a month ago. This seems to also be the same issue with the plugin-twind.js.

### Steps to reproduce

Wait for the cache to expire, load page, with island. Observe load times.

### Expected behavior

As the source hasn't changed and should be already compiled the file should be delivered in milliseconds.

### Environment

"$fresh/": "https://deno.land/x/fresh@1.6.8/"

### Possible solution

_No response_

### Additional context

_No response_

Reproduce the fresh@1.6.8 app after the cache expires, following the reported load sequence for the island JavaScript and plugin-twind.js. Compare delivery times for unchanged compiled assets and determine what causes the multi-second delay; done means the regression is identified and the assets are delivered in milliseconds.

Written by the indexing model from the issue text.