Allow MPT models to return attention weights (#599)
* Allow MPT models to return attention weights
* Update llmfoundry/models/mpt/modeling_mpt.py
Co-authored-by: Daniel King <43149077+dakinggg@users.noreply.github.com>
* Add unit test
* Update tests/test_model.py
Co-authored-by: Daniel King <43149077+dakinggg@users.noreply.github.com>
* Update tests/test_model.py
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Co-authored-by: Daniel King <43149077+dakinggg@users.noreply.github.com>