feat(static): implement Etag rendering for static files

[dominik-air]

Summary of Changes

• Renders ETag for static files and includes it in the Response's headers.
• If If_None_Match header is present in Requests's headers and its ETag matches the file's ETag an HTTP_304 status code is returned.

Related Issues

#2243

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[dominik-air]

I still have to go through the docs to see if any updates are needed there. As of now, I want to check with you if that's the intended implementation.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (4d04e9b) to head (84b9a33).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2333   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           64        64           
  Lines         7725      7748   +23     
  Branches      1071      1074    +3     
=========================================
+ Hits          7725      7748   +23     

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[vytas7]

As I understand, this is work-in-progress, so I didn't review the details, just provided general feedback on how we want to only call fstat() once per file.

[vytas7]

We don't want to run os.fstat() multiple times on the same file handle as it is a real syscall.
We only want to call it once per serving, and save the result in a variable.

[vytas7]

Same as above, we are already calling fstat and handling potential errors elsewhere in this file, we can just reuse the same result.