CUDA: handle OW > 65535 in im2col (2D and 3D) (llama/22944)

CUDA: handle OW > 65535 in im2col (2D and 3D) (llama/22944)

`im2col_cuda` and `im2col_3d_cuda` both dispatch with
`block_nums.y = OW`. CUDA caps grid Y at 65535. Conv1d encoders on
raw 16 kHz audio with T > 65535 (~ 4 s) trip the limit -- e.g. SEANet
at 11 s lands at OW = 176000 -- and the launch returns
`invalid configuration argument`.

Clamp `block_nums.y` to `MIN(OW, MAX_GRIDDIM_Y)` and loop inside the
kernel with stride `MAX_GRIDDIM_Y`. Same in-kernel stride pattern
already used for the z axis (`MAX_GRIDDIM_Z`). Both 2D `im2col_kernel`
and 3D `im2col_3d_kernel` need the same fix. Bit-identical for
OW <= 65535 (single iteration of the new outer loop).

Tested on T4 / Jetson Orin with a SEANet encoder running on 11 s /
16 kHz audio (im2col reaching OW ~ 176000); pre-fix launch returns
`invalid configuration argument`, post-fix runs to completion.
Existing test-backend-ops im2col cases unchanged.