Update NNUE perspectives together
When both perspective accumulators can be updated incrementally, catch up the
lagging perspective and traverse their common suffix once.
During each shared transition:
- decode FullThreats changes once while preserving perspective-specific indices;
- enumerate non-AVX512 PP_3Wide topology once for both perspectives;
- keep HalfKA indices and accumulator arithmetic perspective-specific;
- retain the existing specialized AVX512 PP_3Wide generator.
This preserves feature indices, list ordering, accumulator arithmetic, and the
resulting evaluation.
Passed STC:
https://tests.stockfishchess.org/tests/view/6a63233fc054e285ae028702
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 69632 W: 18217 L: 17881 D: 33534
Ptnml(0-2): 153, 7022, 20132, 7354, 155
closes https://github.com/official-stockfish/Stockfish/pull/7006
No functional change