⚡ Use FrozenDictionarys where possible

[eduherminio]

As explained in https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-8/#frozen-collections, Frozen collections are specialized in reading:

Method	Mean	Ratio
ImmutableDictionaryGets	360.55 us	13.89
DictionaryGets	39.43 us	1.52
FrozenDictionaryGets	25.95 us	1.00

[-5, 0]:

Score of Lynx 1486 - frozen dict vs Lynx 1484 - main: 4529 - 4470 - 3435  [0.502] 12434
...      Lynx 1486 - frozen dict playing White: 2776 - 1721 - 1720  [0.585] 6217
...      Lynx 1486 - frozen dict playing Black: 1753 - 2749 - 1715  [0.420] 6217
...      White vs Black: 5525 - 3474 - 3435  [0.582] 12434
Elo difference: 1.6 +/- 5.2, LOS: 73.3 %, DrawRatio: 27.6 %
SPRT: llr 2.95 (100.3%), lbound -2.94, ubound 2.94 - H1 was accepte