TT buckets: replace InlineArray with explicit struct + pointers

[eduherminio]

#2009 but:

Change implementation to use explicit struct with three fields and access them by casting pointers.

Same bench

Test  | tt/buckets-2-explicitstruct
Elo   | -9.40 +- 5.79 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=2MB
LLR   | -2.30 (-2.25, 2.89) [0.00, 3.00]
Games | 5768: +1497 -1653 =2618
Penta | [148, 742, 1207, 692, 95]
https://openbench.lynx-chess.com/test/2109/