feat: half float support

[XuehaiPan]

Description

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Motivation and Context

Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.
You can use the syntax close #15213 if this solves the issue #15213

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Add half float support.
Resolves #36

Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds core functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of example)

Checklist

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• I have read the CONTRIBUTION guide (required)
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code using make format (required)
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[codecov-commenter]

Codecov Report

Merging #68 (4b7b977) into main (5242e66) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #68      +/-   ##
==========================================
+ Coverage   62.17%   62.20%   +0.03%     
==========================================
  Files          27       26       -1     
  Lines         986      987       +1     
==========================================
+ Hits          613      614       +1     
  Misses        373      373              

Flag	Coverage Δ
unittests	62.20% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
torchopt/_src/accelerated_op/adam_op.py	74.66% <100.00%> (ø)
torchopt/_src/transform.py	80.22% <100.00%> (+0.15%)	⬆️

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