New network, ID `signalis`

[cosmobobak]

This PR adds

• support for king-bucket inference
• an optimisation for king-bucket inference using accumulator caching ("finny tables")
• a new network, signalis, which uses four king buckets and horizontal mirroring.

  ELO   | 5.47 +- 3.57 (95%)
  SPRT  | 40.0+0.40s Threads=1 Hash=128MB
  LLR   | 2.89 (-2.25, 2.89) [0.00, 3.00]
  GAMES | N: 17672 W: 4452 L: 4174 D: 9046
  https://chess.swehosting.se/test/5227/