added utility to plot cmc curve

[ideepankarsharma2003]

Added Utility to Plot CMC Curve

Summary

This PR introduces a utility function to plot the Cumulative Matching Characteristics (CMC) curve and integrates it into the evaluation pipeline.

Changes

• Added plot_cmc() in torchreid/utils/tools.py to generate and save the CMC curve.
• Modified torchreid/engine/engine.py to call plot_cmc() after computing CMC values.
• Ensured the plot is saved at save_dir/cmc_curve.png.

Implementation Details

• plot_cmc() takes CMC values as input and plots the curve using Matplotlib.
• The function supports plotting up to a specified max_rank (default: 50).
• Saves the curve as an image to the provided save_path.

Example Usage

After evaluation, the CMC curve will be automatically generated and saved.

Testing

• Verified that the function correctly plots the curve with sample CMC data.
• Checked that the image is saved properly.

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