Fix 128-bit VQPartialSort/Select, extend+dedup test

[copybara-service[bot]]

Fix 128-bit VQPartialSort/Select, extend+dedup test

Bugfixes:

• 128-bit VQPartialSortStatic/VQSelectStatic: not multiplying k by kLPK
• vqsort_128d.cc: incorrect arg order
• 128-bit HeapSelect: used 1 instead of N1
• safely handle N=1 heap sorts - happens in partial sorts

Test improvements:

• Full coverage for all types/algos via shared TestAnySort/*Verifier
• Centralize VQSORT_SKIP for all tests

Cleanup:

• Use same set of Traits for VQ and Heap, check HWY_SCALAR instead of VQSORT_ENABLED
• Simplify KeyAdapter via hwy::If, use via MakeTraits
• more explicit key vs lane naming
• Avoid duplication of VQ* for SortAscending/SortDescending
• Result -> SortResult to avoid conflict with nanobenchmark.h
• Add+use MaybePoison wrapper to reduce #if