[RFC] “技能水平”的考虑

There was some discussion recently about possible improvements to the implementation of "Skill Level" in Stockfish on discord. @vondele suggested to try eval randomization, in particular interpolation of the NNUE eval with `N(0, RookValueEg)` using some parameter. I've implemented it and tested briefly, but it requires more work to assess the quality of the games played and calibrate the Elo rating. The initial results suggest that it might be a good direction.