⚡ Make TT (wrapper) a readonly struct

[eduherminio]

This implies re-allocating the engine on Hash change, i.e. at the beginning of the execution if a different hash is chosen than the default one, something I'm not a fan of, but some prep for it was done in #1201

Only struct -> #1199

Test  | refactor/tt-outside-of-engine-6-readonly-struct-wrapper
Elo   | 2.15 +- 1.74 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=32MB
LLR   | 2.89 (-2.25, 2.89) [0.00, 3.00]
Games | 65256: +18247 -17844 =29165
Penta | [1542, 7500, 14213, 7759, 1614]
https://openbench.lynx-chess.com/test/974/

Test  | refactor/tt-outside-of-engine-6-readonly-struct-wrapper
Elo   | 1.59 +- 3.69 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=32MB
LLR   | 2.99 (-2.25, 2.89) [-5.00, 0.00]
Games | 14612: +4054 -3987 =6571
Penta | [355, 1685, 3149, 1772, 345]
https://openbench.lynx-chess.com/test/976/