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 75.81%. Comparing base (51d713d) to head (55423c2).

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   75.75%   75.81%   +0.05%     
==========================================
  Files         250      250              
  Lines       19075    19058      -17     
==========================================
- Hits        14451    14448       -3     
+ Misses       4624     4610      -14     

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[dkharms]

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