[SVS] Refactor SVS element size calculations and block size handling

[rfsaliev]

Describe the changes in the pull request

This pull request refactors and improves the way element sizes and block sizes are calculated and used in the SVS storage traits, enhancing clarity and modularity in the code. The changes introduce clearer separation between primary, residual, and secondary element sizes, update the block size calculation to use a new structure, and simplify related test logic.

Which issues this PR fixes

This PR fixes index size estimation issues for SVSIndex by using new blocksize_elements parameter introduced in intel/ScalableVectorSearch#344.

TODO:

• Update SVS shared library binary URLs

Main objects this PR modified

1. SVSIndex
2. SVS tests

Mark if applicable

• This PR introduces API changes
• This PR introduces serialization changes

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Note

Medium Risk
Changes SVS blocked allocation and memory estimation for quantized indexes and bumps the fetched shared library; incorrect blocking could affect memory use or stability, but scope is limited to SVS build/runtime paths.

Overview
Aligns SVS integration with ScalableVectorSearch v0.3.1 (prebuilt tarball URLs in cmake/svs.cmake, including a simpler Clang path that only selects the gcc11 binary when libstdc++ ≥ 11).

LVQ / LeanVec storage now splits byte layout into primary_element_size, residual_element_size, and secondary_element_size, and uses the max of the relevant parts when sizing blocks. SVSBlockSize returns svs::data::BlockingParameters (power-of-two byte block plus blocksize_elements from the VecSim block count), matching upstream blocking behavior and fixing index size estimation.

Tests drop LVQ-specific dimension workarounds in testSizeEstimation (tighter 1% tolerance) and set an explicit blockSize in tiered runGCAPI so GC exercises at least two vector blocks.

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[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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^{Security scan by Jit}

[ethanglaser]

Suggested change

	if(GLIBCXX_VERSION VERSION_GREATER_EQUAL "11")
	set(SVS_URL "https://github.com/intel/ScalableVectorSearch/releases/download/nightly/svs-shared-library-reduced-clang21-gcc11-2026-06-17-1412.tar.gz" CACHE STRING "SVS URL")

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.10%. Comparing base (6ca08ae) to head (92c2189).

⚠️ Current head 92c2189 differs from pull request most recent head fcc801d

Please upload reports for the commit fcc801d to get more accurate results.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #980   +/-   ##
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  Coverage   97.10%   97.10%           
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  Files         141      141           
  Lines        8179     8179           
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  Hits         7942     7942           
  Misses        237      237           

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[alonre24]

LGTM - did we confirm that there is no regression in terms of memory consumption in benchmarks?

[alonre24]

Do we want to merge it as it is (using the nightly version) or bump to an official svs release?