[BUG] cuvsDatasetMakePadded rejects an already-aligned device tensor

Describe the bug

cuvsDatasetMakePadded fails when handed a device tensor whose rows already sit at CAGRA's required stride. The refusal makes sense since it avoids a redundant copy. However, it is not documented in the API, and the C API exposes no way to predict it.

Steps/Code to reproduce bug

1. Allocate a contiguous float32 device matrix whose dimension is a multiple of 4 — e.g. 64 rows × 128 dims. (Contiguous means rowStride == columns, which for 4-byte elements is already the 16-byte-aligned width CAGRA requires.)
2. Wrap it in a DLManagedTensor with device type kDLCUDA.
3. Call cuvsDatasetMakePadded(res, tensor, CUVS_DATASET_MEM_TYPE_DEVICE, &out).
4. Repeat with 127 dims instead of 128 — it succeeds. The boundary is dim % 4 == 0 for float32.

Expected behavior

The dataset contents are copied into newly allocated padded storage, as documented at https://github.com/NVIDIA/cuvs/blob/2140532c5274dfbd9ba1d18c7bbdac15cc7ea93a/c/include/cuvs/core/dataset.h#L62-L63

Actual behavior

CUVS_ERROR, with cuvsGetLastErrorText() returning:

RAFT failure at cpp/include/cuvs/neighbors/common.hpp:1162:
source is device and stride is already correct.
Use make_device_padded_dataset_view() to get a view instead.

Environment details

Not environment specific. Present on main and release/26.08:
https://github.com/NVIDIA/cuvs/blob/2140532c5274dfbd9ba1d18c7bbdac15cc7ea93a/cpp/include/cuvs/neighbors/common.hpp#L1161-L1166

Additional context

The Python workaround is probably the clearest signal that the API is missing something:
https://github.com/NVIDIA/cuvs/blob/2140532c5274dfbd9ba1d18c7bbdac15cc7ea93a/python/cuvs/cuvs/common/dataset.pyx#L73-L89

It matches on the error text, so any rewording of that message turns the workaround into a crash. Rust, Go, and Java have no equivalent workaround and propagate the failure.

Might be related: #2402 (Dataset API C++, C, and language wrapper follow-up), #2394 (Remove dataset views from language wrappers).

Start with cpp/include/cuvs/neighbors/common.hpp:1161-1166 and the C API declaration in c/include/cuvs/core/dataset.h:62-63. Compare the Python handling in python/cuvs/cuvs/common/dataset.pyx:73-89 and review related issues #2402 and #2394. Done should leave the aligned-device-tensor behavior predictable through the API and avoid wrappers depending on matching error text.