Mlflow logging LR duplicate key issue with PostgreSQL DB #190

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### Bug description

**What happened?**
In the anemoi codebase - we use the pytorch lightning MlflowLogger and we hit this error when logging this to a remote server with a postgresql database:

`mlflow.exceptions.RestException: BAD_REQUEST: (raised as a result of Query-invoked autoflush; consider using a session.no_autoflush block if this flush is occurring prematurely)
(psycopg2.errors.UniqueViolation) duplicate key value violates unique constraint "metric_pk"
DETAIL: Key (key, "timestamp", step, run_uuid, value, is_nan)=(lr-AdamW, 1741862947817, 60899, 843c1331fefa436bab56485cfc5bc16e, 0.000322870392593084, f) already exists.`

https://github.com/ecmwf/anemoi-core/blob/main/training/src/anemoi/training/diagnostics/mlflow/logger.py

versions:

```
mlflow 2.22.0
pytorch-lightning 2.5.1
```

### What version are you seeing the problem on?

v2.5

### Reproduced in studio

_No response_

### How to reproduce the bug

```python

```

### Error messages and logs

```
# Error messages and logs here please
```

### Environment

Current environment

```
#- PyTorch Lightning Version (e.g., 2.5.0):
#- PyTorch Version (e.g., 2.5):
#- Python version (e.g., 3.12):
#- OS (e.g., Linux):
#- CUDA/cuDNN version:
#- GPU models and configuration:
#- How you installed Lightning(`conda`, `pip`, source):
```

### More info

_No response_

Start with training/src/anemoi/training/diagnostics/mlflow/logger.py and review how the MlflowLogger records the lr-AdamW metric. Reproduce the reported duplicate-key error against a remote PostgreSQL database using MLflow 2.22.0 and PyTorch Lightning 2.5.1; done means the metric can be logged without the metric_pk violation.

Written by the indexing model from the issue text.