trunk/5545ef3cd14633e943ce244e838eedfb6aff1235: [MPS][BE] Migrate upsample nearest forward to Metal kernels (#186989)

Route the 1D/2D nearest and nearest-exact forward ops to Metal kernels instead of MPSGraph, joining the linear/bilinear/bicubic/3D forward paths that were already Metal. This also fixes a latent MPSGraph correctness bug.

Unify the host-side dispatch so a single templated launcher drives every Metal upsample kernel and UpsampleParams supplies the geometry for all ranks, collapsing the previously duplicated per-rank dispatch overloads.

Backward is intentionally left on MPSGraph: it has no correctness bug and its fused gradient kernel is several times faster than a naive Metal gather.

Co-authored-by: Claude [email protected]

Pull Request resolved: #186989

Approved by: https://github.com/Skylion007, https://github.com/kurtamohler