Add top-k accuracy

[cBournhonesque]

Pull Request Template

Checklist

• Confirmed that run-checks all script has been executed.
• Made sure the book is up to date with changes in this PR.

Related Issues/PRs

#544

Changes

Add top-k accuracy

Testing

Added unit test

[codecov]

Codecov Report

Attention: Patch coverage is 96.77419% with 3 lines in your changes missing coverage. Please review.

Project coverage is 86.24%. Comparing base (f7639bd) to head (695b65c).
Report is 2 commits behind head on main.

Files	Patch %	Lines
crates/burn-train/src/metric/top_k_acc.rs	96.77%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2097      +/-   ##
==========================================
+ Coverage   86.23%   86.24%   +0.01%     
==========================================
  Files         688      689       +1     
  Lines       88465    88558      +93     
==========================================
+ Hits        76285    76379      +94     
+ Misses      12180    12179       -1     

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[laggui]

Thanks for contributing a new metric!

Implementation LGTM 👍