Optimize gives_check for simple variants

[Belzedar94]

Summary

• add a fastCheckDetection flag to Variant that identifies simple rule sets without drops, gating, or other special mechanics
• use the new flag to execute a streamlined Position::gives_check path for normal, promotion, en passant, and castling moves

Testing

• printf "setoption name UCI_Variant value chess position startpos go perft 5 quit " | ./stockfish
• printf "setoption name UCI_Variant value chess position fen r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - go perft 5 quit " | ./stockfish
• ./stockfish bench

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https://chatgpt.com/codex/tasks/task_e_68d1202c875083228d2c6402a0f71365

[Belzedar94]

Standard chess bench:

Pre-patch:
Total time (ms) : 10745
Nodes searched : 6180480
Nodes/second : 575195

===========================

Post-patch:
Total time (ms) : 9860
Nodes searched : 6137642
Nodes/second : 622478

[Belzedar94]

Second speed-up bench comparison:

Pre-patch:
Total time (ms) : 11071
Nodes searched : 6137642
Nodes/second : 554389

===========================

Post-patch:
Total time (ms) : 10121
Nodes searched : 6137642
Nodes/second : 606426