refactor(query engine): simplify proxy <-> stores streams closing

[forshev]

Description

Simplified proxy <-> stores stream closing logic

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.97%. Comparing base (84f72d2) to head (14bb6a3).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
proxy/search/stream_search.go	55.55%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #532      +/-   ##
==========================================
+ Coverage   76.90%   76.97%   +0.06%     
==========================================
  Files         248      248              
  Lines       18856    18839      -17     
==========================================
  Hits        14501    14501              
+ Misses       4355     4338      -17     

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[dkharms]

The invariant holds -- client must read until io.EOF (or any other error).