Create an example for MPZCH

[lizhouyu]

Summary:

Major changes

• Create a mpzch folder under the torchrec/github/examples folder
• Implement a simple SparseArch module with a flag to switch between original and MPZCH managed collision modules
• Profile the running time and QPS for model training(GPU)/inference(CPU)
• Create a notebook tutorial for ZCH basics and the use of ZCH modules in TorchRec

ToDos for OSS

• When the internal torchrec MPZCH module is OSS
  • Remove the BUCK file
  • Replace all the from torchrec.fb.modules in sparse_arch.py to from torchrec.modules

Potential improvement

• Add hash collision counter
• Show profiling results in the Readme file
• Add multi-batch profiling

Reviewed By: aporialiao

Differential Revision: D75570684