FR: wheels that support optional modules

[kiwi3shark]

Hi developers,

torchcomms claims to be a light-weight library, but ncclx seems to be heavy:

14M     /lib/python3.14/site-packages/torchcomms/_comms.cpython-314-x86_64-linux-gnu.so
12M     /lib/python3.14/site-packages/torchcomms/_comms_gloo.cpython-314-x86_64-linux-gnu.so
15M     /lib/python3.14/site-packages/torchcomms/_comms_nccl.cpython-314-x86_64-linux-gnu.so
654M    /lib/python3.14/site-packages/torchcomms/_comms_ncclx.cpython-314-x86_64-linux-gnu.so
12K     /lib/python3.14/site-packages/torchcomms/_comms.pyi
8.0K    /lib/python3.14/site-packages/torchcomms/device_mesh.py
4.0K    /lib/python3.14/site-packages/torchcomms/__init__.py
11M     /lib/python3.14/site-packages/torchcomms/libtorchcomms.so
32K     /lib/python3.14/site-packages/torchcomms/objcol.py
40K     /lib/python3.14/site-packages/torchcomms/__pycache__
376K    /lib/python3.14/site-packages/torchcomms/tests

I wonder if we can just do pip install torchcomms[nccl] to specify the backend such that ncclx can be excluded optionally, and similarly pip install torchcomms[rccl].

Thanks!