fix perplexity logging

[sichu2023]

Replace callback method in logging perplexity with torchmetrics.

Loss curve is shifted by a constant when TP=2 but gradient is not affected and the perplexity value match with the loss curve without TP. This is a previously unidentified problem and will be resolved by another PR.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.17647% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.58%. Comparing base (42d76aa) to head (f6b893a).
⚠️ Report is 565 commits behind head on main.

Files with missing lines	Patch %	Lines
...-packages/bionemo-llm/src/bionemo/llm/lightning.py	88.46%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #622      +/-   ##
==========================================
- Coverage   86.62%   86.58%   -0.05%     
==========================================
  Files         116      116              
  Lines        6961     6931      -30     
==========================================
- Hits         6030     6001      -29     
+ Misses        931      930       -1     

Files with missing lines	Coverage Δ
...ionemo-esm2/src/bionemo/esm2/scripts/train_esm2.py	93.80% <100.00%> (+0.11%)	⬆️
...s/bionemo-geneformer/src/bionemo/geneformer/api.py	100.00% <100.00%> (ø)
...onemo/geneformer/model/finetune_token_regressor.py	60.31% <100.00%> (-0.63%)	⬇️
...packages/bionemo-llm/src/bionemo/llm/model/loss.py	58.53% <100.00%> (-4.11%)	⬇️
...s/bionemo-testing/src/bionemo/testing/lightning.py	100.00% <100.00%> (ø)
...-packages/bionemo-llm/src/bionemo/llm/lightning.py	91.97% <88.46%> (-0.34%)	⬇️

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[farhadrgh]

Left some minor comments, LGTM

[skothenhill-nv]

looks like there are some major diffs that seem unrelated to the change, is there a leaky merge happening here?

[sichu2023]

looks like there are some major diffs that seem unrelated to the change, is there a leaky merge happening here?

Intentionally changes to drop forward output for logging since we are moving to torchmetric now.