Fix importing patch_decoder

[zgeor]

After the latest package fix the patched_decoder cannot be imported. The error when executing the code is

File ~/dev/ml-workspace/timesfm/src/timesfm.py:38
        /dev/ml-workspace/timesfm/src/timesfm.py:36) from praxis.layers import normalizations
        /dev/ml-workspace/timesfm/src/timesfm.py:37) from praxis.layers import transformers
---> /dev/ml-workspace/timesfm/src/timesfm.py:38) from . import patched_decoder
        /dev/ml-workspace/timesfm/src/timesfm.py:39) from utilsforecast.processing import make_future_dataframe
        /dev/ml-workspace/timesfm/src/timesfm.py:41) instantiate = base_hyperparams.instantiate

ImportError: attempted relative import with no known parent package```

This small change will fix the import. I've tested this locally. 

[siriuz42]

Thanks for the fix.