Lazy compute threats
STC: https://tests.stockfishchess.org/tests/view/6acf2360733e627f7058c039
LLR: 2.96 (-2.94,2.94) <0.00,2.00>
Total: 73376 W: 18866 L: 18527 D: 35983
Ptnml(0-2): 88, 7499, 21176, 7836, 89
Compute threats lazily as needed.
Unfortunately, this patch overlaps with https://github.com/official-stockfish/Stockfish/pull/7227 for which I apologize.
I'm more than happy to give all credit to @linrock and make him the author. I think the movegen stuff in the other patch could be tested separately.
No functional change. Written by Claude.
closes https://github.com/official-stockfish/Stockfish/pull/7228
No functional change