[FEA] CAGRA-Q to quantize before graph build

Currently CAGRA-Q does quantization after building the graph. This can certainly improve search performance. But it could be even better to improve build performance if distance computations while building a graph with NN Descent can use lookup tables. The dataset can be quantized before building the graph. Furthermore, it appears that as it stands, if a user uses IVF-PQ as the graph building algorithm with CAGRA-Q, the dataset is quantized twice. I am assuming that some parts from of the product quantized vectors can be reused.

Start by tracing the CAGRA-Q graph-building path and its interaction with NN Descent and IVF-PQ, focusing on where dataset quantization and distance computations occur. Done means evaluating whether quantization can happen before graph construction, lookup tables can support build-time distances, and product-quantized vectors can be reused without double quantization.