Check HTTP status before parsing response body

[ivanauth]

Summary

• When zed validate fetches a URL that returns a non-200 response (e.g. 404), the error page was fed to the schema parser, producing a confusing "invalid yaml" error
• Now checks HTTP status code first and returns a clear error like failed to fetch ...: received HTTP 404
• Strips query params from the error URL to avoid leaking tokens

Closes #671

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.24%. Comparing base (cd9c974) to head (fd35483).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #673      +/-   ##
==========================================
+ Coverage   43.19%   43.24%   +0.04%     
==========================================
  Files          38       38              
  Lines        6035     6040       +5     
==========================================
+ Hits         2607     2612       +5     
  Misses       3163     3163              
  Partials      265      265              

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