Fix replacement option in loss and gradnorm downsampling

[MaxiBoether]

There was an unused replacement option which defaulted to True, which caused multiple keys to be chosen, which caused the storage to crash since it cannot deal with multiple keys in its current implementation. However, it should not have happened in the first place.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.43%. Comparing base (c52a3d6) to head (5f82d0d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #529 +/- ## ========================================== - Coverage 82.43% 82.43% -0.01% ========================================== Files 214 214 Lines 10039 10038 -1 ========================================== - Hits 8276 8275 -1 Misses 1763 1763 ```

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[XianzheMa]

let's just merge this I don't think any problem will be caused

[github-actions[bot]]

^{( % to main) ( % to main)}