test_image_reshape.py: warp/undistort/interp2d tests are empty stubs

Found 2026-08-03 while auditing warpAffine/warpPerspective/remap-based methods for OpenCV 4/5 numeric-drift issues (see #44). `tests/test_image_reshape.py`'s `test_warp`, `test_warp_affine`, `test_warp_perspective`, `test_undistort`, and `test_interp2d` are all empty stubs (`# Add test cases for the decimate method` / `pass`) -- zero real assertions, for five distinct methods in `ImageReshape.py` that wrap `cv2.warpAffine`/`cv2.warpPerspective`/`cv2.remap`/`cv2.undistort`.

`test_rotate` (same file) does have real coverage and was specifically checked against a real OpenCV 5.0.0.93 install as part of #44 -- its one exact-equality assertion (`rotate(0)`, an identity transform) is confirmed safe on both versions, no drift. But the five methods above have no coverage at all to check.

Fix

Write real tests for each: a known input + expected transform (e.g. `warp_affine` with a translation matrix, `undistort` with known distortion coefficients on a synthetic pattern), asserting geometric correctness with a tolerance rather than exact pixel equality -- OpenCV's own migration notes describe revised interpolation between versions 4 and 5, so any assertion here should tolerate small numeric drift by construction, not just by accident.

Beginne in tests/test_image_reshape.py und vergleiche die leeren test_warp-, test_warp_affine-, test_warp_perspective-, test_undistort- und test_interp2d-Stubs mit den entsprechenden Methoden in ImageReshape.py. Verwende anschließend die im Issue vorgeschlagenen synthetischen Eingaben und Transformationen und füge toleranzbasierte Assertions für die geometrische Korrektheit hinzu. Erledigt bedeutet, dass jede Methode eine tatsächliche Abdeckung besitzt, ohne auf exakte Pix elgleichheit zwischen verschiedenen OpenCV-Versionen angewiesen zu sein.