Fix unaligned distance metadata loads [MOD-15303]

[dor-forer]

Summary

• load SQ8, INT8, and UINT8 trailing FP32 metadata through alignment-safe helpers in scalar and SIMD kernels
• make integer normalization and test/reference metadata access alignment-safe
• repair the SQ8-FP32 benchmark's storage/query argument order and array teardown
• add explicit odd-dimension SQ8-FP32 regression coverage

Root cause

Trailing FP32 metadata follows byte-width vector payloads. For dimensions not divisible by four, casting payload + dimension to float * creates a misaligned pointer and undefined behavior. The SQ8-FP32 benchmark also supplied its FP32 query and SQ8 storage in reverse order, producing an out-of-bounds read.

Impact

Odd-dimensional SQ8/SQ8-FP32 and INT8/UINT8 cosine distance calculations no longer rely on misaligned FP32 loads, including dispatched SIMD implementations and strict-alignment architectures.

Validation

• ./check-format.sh
• alignment/undefined sanitizer: 520 SQ8/SQ8-FP32/INT8/UINT8 distance tests
• alignment/undefined sanitizer: affected component, INT8, UINT8, and index utility tests
• AddressSanitizer + undefined sanitizer: SQ8-FP32 dimension-100 benchmark matrix (available AVX2-FMA, AVX2, SSE4, and scalar paths)

Deterministic alignment regression proof

Built the regression test with Clang 18.1.8 and fatal AddressSanitizer/alignment sanitization:

• PR c724d32b: exited 0; SpacesTest.SQ8_FP32_odd_dim_unaligned_metadata_test passed.
• Main dd6879e8, with only the test and safe reference-helper changes applied: exited 1.
• UBSan reported the old production load in SQ8_FP32_InnerProduct_Impl:

src/VecSim/spaces/IP/IP.cpp:61:27:
runtime error: load of misaligned address 0x503000025691
for type 'const float', which requires 4 byte alignment

The forced address ends in ...691, proving it is not four-byte aligned. The sanitizer stack traces the failure from SQ8_FP32_InnerProduct_Impl directly to the odd-dimension regression test.

Jira: MOD-15303

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Note

Medium Risk
Touches hot-path distance math across many SIMD backends; behavior should be equivalent but incorrect offset math would skew all SQ8/integer cosine results for affected dimensions.

Overview
Fixes undefined behavior when VecSim reads trailing FP32 metadata (SQ8 min/delta/sum, INT8/UINT8 cosine norms) after byte-sized payloads: odd dimensions leave metadata at addresses that are not 4-byte aligned, so reinterpret_cast<const float *> loads were unsafe.

Scalar and SIMD inner product / L2 paths for SQ8↔FP32, SQ8↔SQ8, and INT8/UINT8 cosine now use load_unaligned with byte offsets (sq8::* * sizeof(float)). Integer normalization writes the stored norm via memcpy instead of a misaligned float store. Reference helpers, unit tests, and the SQ8-FP32 benchmark follow the same pattern; the benchmark also swaps storage vs query to match API argument order and fixes delete[].

Adds SQ8_FP32_odd_dim_unaligned_metadata_test to exercise deliberately misaligned storage blobs against scalar and dispatched kernels.

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