feat(http): add cleanUrls option to serveDir

[lowlighter]

This PR introduces a new cleanUrls option to serveDir function

It is inspired from a common pattern where you don't have to specify the html extension to serve a page.
(e.g. deno.com/blog, github.com/denoland/std, ..., some hosters such as Vercel also propose a similar feature)

Considerations:

• Only .html is handled by this new option, for more advanced usage user would need to use their own routing
  • The reasoning for what it'd be supported natively by std is that it's a really common use case, and it's actually not that easy to get a simple workaround (e.g. if you use route(request), as Request are immutable you'll need to do some shenanigans to trim extensions, catch the 404 to retry with it, etc.)
  • It'd be an extremely nice QOL and since it's gated behind an option would not be a breaking change and would not hinder performances of existing apps
• If the path without extension "shadows" another file or directory, the latter takes precedences over the otherwise cleaned url aliased file

Closes #6232

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.51%. Comparing base (b1b8279) to head (857c391).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6231      +/-   ##
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- Coverage   96.52%   96.51%   -0.01%     
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  Files         534      534              
  Lines       40976    40986      +10     
  Branches     6134     6138       +4     
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+ Hits        39551    39559       +8     
- Misses       1383     1385       +2     
  Partials       42       42              

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[lowlighter]

I'm closing it for now, but I still think this patch would be a nice QOL, especially since it doesn't have that much maintenance/overhead, but this may need further discussion as pointed on the discord server since opinions seems to be diverging.

---

Feedback from the discord:

It's common as a "framework feature", but for file server (like apache) you usually need either rewriting urls or set the default mime type to text/html

A workaround is to change the file structure to use folder + index.html instead but although it works it makes you change the way you organize file rather than your code (which shouldn't be, the file structure may be required to be a certain way depending on your use case)