Add split copy

[metascroy]

This adds coremltools support for split_copy, the copy variant of split. Many view ops in coremltools already register the copy variant as an alias, e.g.,

view: https://github.com/apple/coremltools/blob/main/coremltools/converters/mil/frontend/torch/ops.py#L2316 permute: https://github.com/apple/coremltools/blob/main/coremltools/converters/mil/frontend/torch/ops.py#L1011

But it looks like for split this was missed.

Similar PR for transpose_copy: https://github.com/apple/coremltools/pull/2556

[metascroy]

cc @YifanShenSZ

[TobyRoseman]

Thanks @metascroy for the pull request. Can you add a unit test?

[YifanShenSZ]

CI 🔴 https://gitlab.com/coremltools1/coremltools/-/commit/35edb4d17ab9eb1cd95f09f3c3dba7db9e157f75/pipelines

because we support torch up to 2.7.1 😮‍💨 please rebase on top of latest main to pick up https://github.com/apple/coremltools/pull/2591