Fix MLflow test by safely logging artifact and creating experiment if missing

[Nafeessidd1]

This PR addresses issue #165 by:

• Creating the MLflow experiment if it doesn't exist in the mlflow_run fixture
• Fixing test_mlflow_artifacts by safely ending any active run before starting one
• Logging a dummy artifact to ensure client.list_artifacts(run_id) returns a non-empty list
• Minor cleanup for robust test behavior

All tests are passing locally ✅

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.37%. Comparing base (931133c) to head (2abe9b1).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #166   +/-   ##
=======================================
  Coverage   95.37%   95.37%           
=======================================
  Files          26       26           
  Lines        1189     1189           
=======================================
  Hits         1134     1134           
  Misses         55       55           

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