🔍 Don't always stop search when a mate is found

[eduherminio]

Take into account 50 moves draw rule when considering stopping a search because of mate found: if our engine found a mate sequence but that mate sequence won't win the game due to the 50 moves rule (or close to it), keep searching for a better mate

Example of game where a victory was spoiled by this:
https://lichess.org/qTZZzk7b

[-3. 1], 8+0.08, usual adj.

Score of Lynx-dont-always-stop-search-on-mate-3228-win-x64 vs Lynx 3221 - main: 6393 - 6296 - 7799  [0.502] 20488
...      Lynx-dont-always-stop-search-on-mate-3228-win-x64 playing White: 4580 - 1805 - 3859  [0.635] 10244
...      Lynx-dont-always-stop-search-on-mate-3228-win-x64 playing Black: 1813 - 4491 - 3940  [0.369] 10244
...      White vs Black: 9071 - 3618 - 7799  [0.633] 20488
Elo difference: 1.6 +/- 3.7, LOS: 80.5 %, DrawRatio: 38.1 %
SPRT: llr 2.9 (100.3%), lbound -2.25, ubound 2.89 - H1 was accepted