[FEA] Remove cuvsCagraCompressionParams and only use cuvsProductQuantizerParams

TLDR: We have repetitive params that do the same thing.
CompressionParams/cuvsCagraCompressionParams (in index header file c/include/cuvs/neighbors/cagra.h)
PqParams/cuvsProductQuantizerParams (in quantizer header file c/include/cuvs/preprocessing/quantize/pq.h)

Historical reason:
CompressionParams was historically a property of the index and a duplicate of pqParams/cuvsProductQuantizerParams since index previously constructed a compressed dataset internally (hence it was a property of index).

However, now since we added the dataset API which leaves it to the user to construct a compressed quantized dataset themselves outside of the index through a dataset factory, this decouples compression from the index (compression is no longer an index property).

Solution: delete CompressionParams and only use pqParams/cuvsProductQuantizerParams (which is a dataset property and is located in the quantizer header file).

Start with c/include/cuvs/neighbors/cagra.h and c/include/cuvs/preprocessing/quantize/pq.h, then trace references to CompressionParams, cuvsCagraCompressionParams, PqParams, and cuvsProductQuantizerParams. Review the affected index and dataset API usage before removing the duplicate compression parameters. Done means the index no longer exposes CompressionParams and the product-quantizer parameters are used consistently.