fix: only original value destroy if the new value is not a stream

[yowainwright]

Description

This PR adds a minimal fix + tests for #1913.
Thanks @nuintun for their observation and solutions.

Checklist

• I have ensured my pull request is not behind the main or master branch of the original repository.
• I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• I have written a commit message that passes commitlint linting.
• I have ensured that my code changes pass linting tests.
• I have ensured that my code changes pass unit tests.
• I have described my pull request and the reasons for code changes along with context if necessary.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.90%. Comparing base (1c642f4) to head (07c0c49).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1914   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files           9        9           
  Lines        2081     2084    +3     
=======================================
+ Hits         2079     2082    +3     
  Misses          2        2           

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[Copilot]

Pull Request Overview

This PR fixes an issue where setting res.body to a new stream would incorrectly destroy the original stream, breaking middleware patterns that wrap streams (like compression middleware). The fix prevents destroying the original stream when the new value is also a stream, while still cleaning up streams when replaced by non-stream values.

Key Changes:

• Modified stream cleanup logic to only destroy the original stream when replaced by a non-stream value
• Updated test expectations to reflect that streams should not be destroyed when replaced by other streams
• Added a new test case demonstrating the wrapping stream middleware pattern

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/response.js	Added conditional check to prevent destroying original stream when new value is also a stream
tests/response/body.test.js	Updated test expectations and added new test case for wrapping stream middleware pattern

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