fix: potential body error race

[danielgtaylor]

This attempts to fix a hard-to-repro race condition when returning an error due to marshaling that includes a reference to the body bytes that will get returned to the pool for re-use before the output is done. The fix here is to cast the bytes to a string, which creates a copy that is safe to reference later.

Fixes #685.

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.77%. Comparing base (5c03160) to head (1182cc1).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #687   +/-   ##
=======================================
  Coverage   92.77%   92.77%           
=======================================
  Files          22       22           
  Lines        4915     4915           
=======================================
  Hits         4560     4560           
  Misses        308      308           
  Partials       47       47           

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