Revert "Merge pull request #10069 from Turbo87/publish-stream"

[Turbo87]

This reverts PR #10069 and resolves #10098.

The 503 error returned by Heroku is apparently caused by our usage of the "legacy router" on Heroku. When using "Heroku Router 2.0" the 503 error is gone, but now AWS Cloudfront starts acting up and returns 500 errors instead.

From the looks of it this appears to be a bug in Cloudfront, which does not seem to be able to handle HTTP responses while the request hasn't fully been received yet?

Unfortunately, that means we have to revert the semi-streaming publish endpoint for now and buffer everything upfront again until we either figure out how to make this work in Cloudfront, or switch to a different CDN for the crates.io API.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.47%. Comparing base (a27a914) to head (baa3411).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10102      +/-   ##
==========================================
- Coverage   89.47%   89.47%   -0.01%     
==========================================
  Files         294      294              
  Lines       31254    31224      -30     
==========================================
- Hits        27964    27937      -27     
+ Misses       3290     3287       -3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.