Move CA to albef dir

[ankitade]

Summary:
Moving cross attn to albef since its only used by albef

Test plan:
pytest tests/models/albef/test_albef.py

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (1940623) 68.65% compared to head (f36b1d4) 68.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #437      +/-   ##
==========================================
+ Coverage   68.65%   68.66%   +0.01%     
==========================================
  Files         169      169              
  Lines       11350    11355       +5     
==========================================
+ Hits         7792     7797       +5     
  Misses       3558     3558              

Impacted Files	Coverage Δ
tests/modules/layers/test_transformer.py	100.00% <ø> (ø)
torchmultimodal/modules/layers/transformer.py	98.66% <ø> (-0.56%)	⬇️
tests/models/albef/test_albef.py	100.00% <100.00%> (ø)
torchmultimodal/models/albef/multimodal_encoder.py	98.57% <100.00%> (+5.23%)	⬆️

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@ankitade has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@ankitade merged this pull request in 82c1dc2.