Reject truncated JPEG image buffers

[bghira]

This pull request improves the robustness of JPEG decoding in the imdecode function by adding explicit validation to detect truncated or malformed JPEG files before attempting to decode them. It also introduces comprehensive tests to ensure truncated or manipulated JPEGs are correctly rejected and that trailing bytes after a valid JPEG are tolerated.

JPEG validation improvements:

• Added a validate_jpeg_complete function to the imdecode implementation in cv_compat.rs that parses JPEG markers to ensure the image is complete and not truncated before decoding. This function checks for the presence and correct order of JPEG markers, including the end-of-image marker, and rejects files with missing or misplaced markers. [1] [2]

Testing enhancements:

• Added new Rust tests in tests.rs to verify that truncated JPEGs are rejected, JPEGs with marker bytes in metadata are not incorrectly accepted as complete, and valid JPEGs with trailing non-image data are still accepted. [1] [2]
• Added a Python binding test to ensure that truncated JPEGs are rejected by the Python interface as well, raising an appropriate error.