[gouyt13]

RaBitQ 0.7.0 introduces modular core/FastScan targets for lighter integration. This PR upgrades zvec from 0.3.8 and replaces its custom build configuration and LUT patch with these upstream targets.

Update header paths, reuse query scratch through SplitBatchQuery::reset, and use consistent Eigen alignment settings across RaBitQ and Turbo/OPQ. Existing index padding and platform enablement are preserved; RaBitQ ANN indexes and OpenMP remain disabled.

Validated on Linux x86-64 with GCC 14.3, Release, default AUTO_DETECT_ARCH=ON, and RaBitQ native tuning disabled:

• Static/shared builds and 42 targeted tests pass.
• 39 direct tests pass under ASan/UBSan with leak detection; persistence and mixed Eigen consumer probes also pass.
• Across 16 compatibility fixtures, all 3,200 ordered result IDs match, with maximum score difference below 8e-6.
• The Linux CPython 3.13 wheel builds, installs, and passes 688 selected Python tests, including IVF/HNSW RaBitQ and bundled-resource checks. Imported extension hashes match the wheel.
• Formatting, clang-tidy on changed translation units, and diff checks pass.

Full database sanitizer checks remain incomplete due to duplicate core linkage and an existing Arrow scalar downcast in SegmentImpl::fetch. Other Python versions, manylinux packaging, and Windows/macOS/ARM checks have not been run locally.

[CLAassistant]

All committers have signed the CLA.

[egolearner]

LGTM