Remove dependency of backend CPU and fix CI

• Remove Backend CPU from CMakeLists.txt, setup.py and CI
• Add include shared script in build CI
• Add empty python requirements.txt for CI
• Generate random matrix in tests instead of loading an image from a path for CI on OVH
• Update Test to comply with opencv::convertNonZero that requires single channel array in v4.2 (https://docs.opencv.org/4.2.0/d2/de8/group__core__array.html#gaa4b89393263bb4d604e0fe5986723914)