Make index blocksize flexible

[razdoburdin]

This PR adds ability to set custom index blocksize
Reopening of #235

[rfsaliev]

Hi!
Thank you for the PR.
Looks good but I see some issues:

• Extra dependencies on SVS internal headers (svs/lib/...) added to the runtime API in index_blocksize.h - I would avoid such dependencies by replacing:
  • usage svs::lib::PowerOfTwo with just a size_t BlockSizeExponent(); and size_t BlockSizeBytes() const { return 1 << blocksize_exp_; }
  • replace IndexBlockSize .ctor with a static factory method e.g. static Status IndexBlockSize::make(size_t blocksize_exp) noexcept; - as it was made to other runtime API classes.
• The DynamicVamanaIndex::add(..., IndexBlockSize); method has unclear semantic, because blocksize argument can be applied at the first call only, but not at subsequential calls.

Instead I would propose to setup block size in a build() method:

• One of solutions can be blocksize field in VamanaIndex::BuildParams - but it seems block size makes no sense in non-dynamic indices.
• Another option: define a dedicated structure with parameters for dynamic indices: e.g. blocksize, reuse_empty_slots, etc.

[rfsaliev]

Please also read my standalone comment to the PR as well.

[rfsaliev]

Please avoid SVS internals dependencies in SVS Runtime

[razdoburdin]

done

[rfsaliev]

SVS runtime API should be noexcept

[razdoburdin]

the IndexBlockSize structure is removed

[rfsaliev]

Please convert SVS Runtime API data types (IndexBlockSize) to SVS internal type (PowerOfTwo) here.
As it was made for data argument

[rfsaliev]

I do not think it makes sense to modify SVS internals just to implement a query for SVS runtime API

[razdoburdin]

fixed
The getter now calls for parameter filed, not the SVS internals

[razdoburdin]

Thanks for comments.

I have modified the PR, according to your request:

1. I have added a new structure VamanaIndex::DynamicIndexParams, being passed to build() constructor. It contains the only field blocksize_exp now, but it can be expanded.
2. In this case the dedicated IndexBlockSize is no longer needed, so I have removed it. The DynamicVamanaIndex class is no responsible for checking the validity of input parameters by calling check_params method.