Replace nnueComplexity with simple_eval equivalent
This greatly eases future network arch simplifications, namely removing its `psqt` component.
This PR squashes and supersedes #7071, the first version, and #7105, the simplified form which was built atop the first version.
The vast majority of the credit goes to Tony, and Dubslow assisted in simplifying and admin.
The first version tests:
Passed STC: https://tests.stockfishchess.org/tests/view/6a72671d2cf557d58a2e1d5b
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 312288 W: 80020 L: 80103 D: 152165
Ptnml(0-2): 473, 37193, 81228, 36444, 806
Passed LTC: https://tests.stockfishchess.org/tests/view/6a7a2a278b9c2482ffa9e00b
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 189792 W: 49500 L: 49452 D: 90840
Ptnml(0-2): 33, 20317, 54212, 20237, 97
Meanwhile, this simplified form had its STC test against the first version, while the second LTC was directly against then-master.
Passed STC: https://tests.stockfishchess.org/tests/view/6a85694a9960adfadf924227
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 46624 W: 11969 L: 11764 D: 22891
Ptnml(0-2): 83, 5382, 12176, 5589, 82
Passed LTC: https://tests.stockfishchess.org/tests/view/6a8778415b1b38ebda864f3e
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 250080 W: 64691 L: 64704 D: 120685
Ptnml(0-2): 68, 26659, 71582, 26680, 51
closes https://github.com/official-stockfish/Stockfish/pull/7187
Bench: 1495562