Add a new Layer "DataCell" to manage data access

[LHT129]

I think high level index should ignore the specific implement of quantization and io type, So the quantization and io components can be managed by new layer DataCell which provide different data access interface to the index layer. just like the following show

Layer	Description	Implement
Index Layer	ANN algorithm & architecture.	Graph (HNSW,NNDescent) + Reorder, IVF(PQ,SQ,fastscan), HNSW_IVF, MultiIndex ......
DataCell Layer	data access, use quantization, io and others	FlattenDC, GraphNeighborhoodDC, MixtureDC .......
Operator Layer	quantizations, IO and other basic components	PQ,SQ,MemoryIO,SSDIO,......

this abstract layered approach may facilitate scalability and code reuse
currently we only have index layer, so the issue will provide Datacell Layer and Operator Layer in this feature.
the related pull requests:

• add some basic structure for quantizer, io and simd operators #25
• add sq8 classical quantizer and simd operators #34
• add data cell structure, flatten as example #37
• add sq4 quantizer and simd operators #41
• [WIP] Mix data cell #35
• Add io component #59
• Support io direct read cross blocks #60
• Update quantization test & Add Serialize method #61
• Add Graph Interface #62
• enable allocator for io #79
• enable allocator for quantizers #80
• add graph_datacell and sparse_graph_datacell #96
• add hgraph param #111
• introduce hgraph #114
• add hgraph test & fix #125
  todo tasks:
• support mixture DataCell
• adapt Graph DataCell for HNSW
• implement HNSW + SQ4 + SQ8 Index

[LHT129]

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