CUDA: Various fixes to `cpy.cu` (llama/25000)

CUDA: Various fixes to `cpy.cu` (llama/25000)

* Add failing test-case to test-backend-ops

Extracted from https://github.com/ggml-org/llama.cpp/issues/24072

* Minimize repro with help of AI

N = 8 * (65535 - 1) + 1 = 524273

* Port and adjust workaround from https://github.com/LostRuins/koboldcpp/commit/0ba798341e0c70517cb226cb63c966b086a3b5b3

Fall-back should share code, also relax y-z constraint to be inclusive

* Add test-case + fallback also for y dim

* Fix x-guards which is 2^{31}-1, so inlusive of INT_MAX

* Fix overflow problems for transposed copy kernel