fix: fix fetch() trace span

[MrCroxx]

What's changed and what's your intention?

Please explain IN DETAIL what the changes are in this PR and why they are needed. :D

As title.

e.g.

Checklist

• I have written the necessary rustdoc comments
• I have added the necessary unit tests and integration tests
• I have passed make all (or make fast instead if the old tests are not modified) in my local environment.

Related issues or PRs (optional)

#577

[codecov]

Codecov Report

Attention: Patch coverage is 86.48649% with 5 lines in your changes missing coverage. Please review.

Project coverage is 86.07%. Comparing base (2146ab6) to head (d0becdb).

Files	Patch %	Lines
foyer-common/src/trace.rs	77.27%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #586      +/-   ##
==========================================
- Coverage   86.21%   86.07%   -0.14%     
==========================================
  Files          59       59              
  Lines        7602     7570      -32     
==========================================
- Hits         6554     6516      -38     
- Misses       1048     1054       +6     

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