Torch tensors throw 'input not a numpy array' on some classes, like faiss.Clustering

# Summary

# Platform

OS: Ubuntu 20.04

Faiss version: 1.7.1

Installed from: anaconda by `conda install -c pytorch -c conda-forge faiss-gpu`

Faiss compilation options:

Running on:
- [ ] CPU
- [x] GPU

Interface:
- [ ] C++
- [x] Python

# Reproduction instructions
Example 1:
> Fixed by importing `faiss.contrib.torch_utils`. But that's not too obvious from wiki documentation.
```py
import faiss.contrib.torch_utils
import faiss, torch
D = 32
bank = torch.randn(1000, D)
query = torch.randn(100, D)
res = faiss.StandardGpuResources()
idx = faiss.index_factory(D, 'IVF384,Flat')
gidx = faiss.index_cpu_to_gpu(res, 0, idx)
gidx.train(bank) # fails
gidx.train(bank.cuda()) # fails
gidx.train(bank.numpy()) # succeeds
gidx.add(bank) # fails
gidx.add(bank.cuda()) # fails
# ... etc.
```

Example 2:
> Follows https://github.com/facebookresearch/faiss/blob/main/faiss/gpu/test/torch_test_contrib_gpu.py#L255
> But fails even with `import faiss.contrib.torch_utils`.
```py
import faiss.contrib.torch_utils
import faiss, torch
D = 32
bank = torch.randn(1000, D)
query = torch.randn(100, D)
res = faiss.StandardGpuResources()
clus = faiss.Clustering(D, 384)
clus.verbose = True
clus.niter = 20
cfg = faiss.GpuIndexFlatConfig()
cfg.useFloat16 = True
cfg.device = 0
index = faiss.GpuIndexFlatIP(res, D, cfg)
clus.train(bank, index)
# Fails by
# ValueError: input not a numpy array
```