feat(http/unstable): `parallel-file-server` module

[iuioiua]

Closes #5681

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 9.37500% with 29 lines in your changes missing coverage. Please review.

Project coverage is 96.24%. Comparing base (a81742a) to head (c56fa0b). Report is 23 commits behind head on main.

Files	Patch %	Lines
http/_get_server_args.ts	6.66%	28 Missing :warning:
http/file_server.ts	50.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5786      +/-   ##
==========================================
- Coverage   96.26%   96.24%   -0.02%     
==========================================
  Files         481      482       +1     
  Lines       38738    38743       +5     
  Branches     5615     5615              
==========================================
- Hits        37291    37290       -1     
- Misses       1406     1412       +6     
  Partials       41       41              

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[kt3k]

Should we add some warning about that the script is still unstable?

[iuioiua]

There are multiple ways we can go about having a HTTP file server work in parallel. I'm not sure this approach is best as I'm not sure having a whole new endpoint is the best way to go. Alternatively, we could have --parallel just work with Deno.serve(), which would make this work a lot simpler.