Add model EMA (Exponential Moving Average)

[sokovninn]

This pull request introduces a new Exponential Moving Average (EMA) callback for model training, along with its integration and corresponding unit tests. The main changes include the addition of the EMACallback class, its registration, and tests to ensure its functionality.

New EMA Callback

• luxonis_train/callbacks/ema.py: Added the EMACallback class, which includes methods for initializing the EMA, updating EMA weights, and handling checkpoint saving/loading. This class helps in maintaining a moving average of model parameters to potentially improve model performance.

Integration

• luxonis_train/callbacks/__init__.py: Registered the EMACallback in the CALLBACKS registry and added it to the __all__ list for proper module export. [1] [2] [3]

Unit Tests

• tests/unittests/test_callbacks/test_ema.py: Added unit tests for the EMACallback to verify its initialization, batch update, checkpoint saving/loading, and validation epoch handling.

[klemen1999]

Overall LGTM, let's also add it do the docs (callback README)

[codecov]

Codecov Report

Attention: Patch coverage is 93.84615% with 8 lines in your changes missing coverage. Please review.

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✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
luxonis_train/callbacks/ema.py	89.18%	8 Missing ⚠️

Additional details and impacted files

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[kozlov721]

LGTM