[Bug] `DataFrame.append()` is deprecated in metrics.py with pandas >= 2.0

The current implementation of `metrics.py` uses the deprecated method `DataFrame.append()`, which was removed in pandas 2.0+. Running the script with recent versions of pandas throws the following error:

The problematic line is around line 107 in `metrics.py`:

- Suggested Fix
`df_all = pd.concat([df_all, df[["sanity_check"]]], ignore_index=True)`