perfect: Optimize random number generation by using static variables

Modified the `chooseRandom` function to declare `std::random_device` and
`std::mt19937` as static variables. This change ensures that these objects are
initialized only once, reducing the overhead of repeatedly creating them on
each function call. This optimization is expected to improve performance by
approximately 0.02%. This aligns with practices in ggevay's original Visual Basic
code, where the random generator was a static (Shared) variable.

Reference: ggevay/malom#3 (comment)
Change-Id: Ic3b461caf52f533d4bbd5dc29ada65172d5c4450

src/perfect/perfect_player.cpp

@@ -444,9 +444,10 @@ int PerfectPlayer::NGMAfterMove(const GameState &s, AdvancedMove &m)
 template <typename T>
 T PerfectPlayer::chooseRandom(const std::vector<T> &l)
 {
+    static std::random_device rd;
+    static std::mt19937 gen(rd());
+
     if (gameOptions.getShufflingEnabled()) {
-        std::random_device rd;
-        std::mt19937 gen(rd());
         std::uniform_int_distribution<> dis(0, static_cast<int>(l.size() - 1));
         return l[dis(gen)];
     }