Added Sparse/Lazy Adam optimizer

[atreyamaj]

Description

Added the Sparse Adam optimizer, also known as the Lazy Adam optimizer.

Referencing #2478

This change requires the Tensorflow Addons dependency, which is an official extension of the Tensorflow library. This PR is intended to be merged after #2488

Type of change

Please check the option that is related to your PR.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • In this case, we recommend to discuss your modification on GitHub issues before creating the PR
• Documentations (modification for documents)

All tests for test_optimizers.py are passing.

The warnings seem to be unrelated to the added code.

Checklist

• My code follows the style guidelines of this project
  • Run yapf -i <modified file> and check no errors (yapf version must be 0.22.0)
  • Run mypy -p deepchem and check no errors
  • Run flake8 <modified file> --count and check no errors
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New unit tests pass locally with my changes
• I have checked my code and corrected any misspellings

@rbharath @alat-rights @peastman @ncfrey

P.S. I have made this PR a draft PR at the moment. If the addition of TF_Addons is alright, I will change it to an Open PR.

[codecov-commenter]

Codecov Report

Merging #2493 (a3df318) into master (dd8665e) will increase coverage by 0.00%.
The diff coverage is 88.23%.

@@           Coverage Diff           @@
##           master    #2493   +/-   ##
=======================================
  Coverage   85.77%   85.78%           
=======================================
  Files         309      309           
  Lines       27454    27488   +34     
=======================================
+ Hits        23550    23580   +30     
- Misses       3904     3908    +4     

Impacted Files	Coverage Δ
deepchem/models/tests/test_optimizers.py	94.05% <86.66%> (-1.29%)	⬇️
deepchem/models/optimizers.py	91.27% <89.47%> (-0.27%)	⬇️

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[rbharath]

Code looks good on my end! Might be good to have @peastman take a quick look as well since he's been reviewing the other optimizer PRs

[rbharath]

Ah my bad, sorry just noticed this is a WIP. Let me know when this is ready to review!

[atreyamaj]

Ah my bad, sorry just noticed this is a WIP. Let me know when this is ready to review!

@rbharath It should be ready to review 😅

I marked it as a draft due to the additional dependency temporarily.

I'll go ahead and mark it open for review now.

[peastman]

Looks good!

[peastman]

Except yapf is complaining. Can you run it on test_optimizers.py?

[atreyamaj]

Except yapf is complaining. Can you run it on test_optimizers.py?

Sorry about that, I've committed the YAPF reformatting. @peastman

[rbharath]

Going to go ahead and merge in!