ccalib: add k3 radial distortion support for omnidir model

[nechami795]

Summary

Add support for an additional radial distortion coefficient (k3) to the omnidirectional camera model in ccalib.

Details

• Extend omnidir distortion model to accept both 4- and 5-parameter distortion vectors.
• Ensure full backward compatibility when k3 = 0.
• Update projectPoints, undistortPoints, and initUndistortRectifyMap to handle k3.
• Add comprehensive unit tests covering:
  • backward compatibility
  • functional impact of k3
  • calibration quality improvement when true k3 ≠ 0

Tests

• Added new tests under modules/ccalib/test validating:
  • identical behavior for 4 coeffs vs 5 coeffs with k3 = 0
  • measurable change when k3 is non-zero
  • lower reprojection RMS when calibrating with 5 parameters on synthetic data

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[asmorkalov]

The tests you added are very soft and check mostly nothing. Please enhance the tests with real coordinates / distortion coefficients check.

[nechami795]

The tests you added are very soft and check mostly nothing. Please enhance the tests with real coordinates / distortion coefficients check.

Thank you for the comment.
I've run full process with real coordinates, but I did that from a separate standalone .cpp, not from tests.
Right now I am improving the code, will make additional test later.