fix resize interpolation contract adherence

[bghira]

This pull request refactors and improves the image resizing functionality using OpenCV, making interpolation methods explicit and configurable for both single and batch image resizing operations. It also optimizes the Python binding for batch luminance calculation by parallelizing the computation. Additional tests are added to ensure correct behavior of the new interpolation logic.

OpenCV image resizing improvements:

• Refactored the OpenCVBatchProcessor to allow specifying the interpolation method (e.g., INTER_LINEAR, INTER_LANCZOS4) for both single and batch image resizing. This makes the resizing behavior explicit and configurable. (src/opencv_ops.rs, [1] [2] [3] [4] [5] [6]
• Updated the resize_bilinear_opencv and resize_lanczos4_opencv functions to explicitly pass the correct interpolation method to the underlying resizing implementation. (src/opencv_ops.rs, [1] [2]

Performance and Python bindings:

• Optimized the batch_calculate_luminance Python binding by using Rayon for parallel computation, improving performance when processing multiple images. (src/python_bindings.rs, src/python_bindings.rsL955-R968)

Testing enhancements:

• Added a new test to verify that bilinear and Lanczos4 resizing use different OpenCV interpolation modes, and that both single and batch resizing paths produce consistent results. Also updated imports in the test module for clarity. (src/tests.rs, [1] [2]

[Copilot]

Pull request overview

This PR makes OpenCV resize interpolation behavior explicit (so “bilinear” and “Lanczos4” paths actually use the correct OpenCV interpolation modes), adds a regression test for that contract, and parallelizes the Python batch luminance binding.

Changes:

• Refactors OpenCV resize internals to accept an explicit interpolation mode, defaulting batch image resize to INTER_LINEAR and adding a Lanczos4 batch path.
• Updates the single-image OpenCV resize wrappers to pass the correct interpolation constants.
• Parallelizes batch_calculate_luminance in Python bindings using Rayon (with the GIL released) and adds an OpenCV interpolation contract test.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/opencv_ops.rs	Makes interpolation explicit for single and batch OpenCV resizing; fixes bilinear/Lanczos4 wrappers to use correct modes.
src/python_bindings.rs	Parallelizes batch luminance calculation using Rayon and py.allow_threads.
src/tests.rs	Adds a regression test ensuring bilinear vs Lanczos4 produce different results and that batch vs single paths match.

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