Refactor Network Usage

Continuing from PR #4968, this update improves how Stockfish handles network
usage, making it easier to manage and modify networks in the future.

With the introduction of a dedicated Network class, creating networks has become
straightforward. See uci.cpp:
```cpp
NN::NetworkBig({EvalFileDefaultNameBig, "None", ""}, NN::embeddedNNUEBig)
```

The new `Network` encapsulates all network-related logic, significantly reducing
the complexity previously required to support multiple network types, such as
the distinction between small and big networks #4915.

Non-Regression STC:
https://tests.stockfishchess.org/tests/view/65edd26c0ec64f0526c43584
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 33760 W: 8887 L: 8661 D: 16212
Ptnml(0-2): 143, 3795, 8808, 3961, 173

Non-Regression SMP STC:
https://tests.stockfishchess.org/tests/view/65ed71970ec64f0526c42fdd
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 59088 W: 15121 L: 14931 D: 29036
Ptnml(0-2): 110, 6640, 15829, 6880, 85

Compiled with `make -j profile-build`
```
bash ./bench_parallel.sh ./stockfish ./stockfish-nnue 13 50

sf_base =  1568540 +/-   7637 (95%)
sf_test =  1573129 +/-   7301 (95%)
diff    =     4589 +/-   8720 (95%)
speedup = 0.29260% +/- 0.556% (95%)
```

Compiled with `make -j build`
```
bash ./bench_parallel.sh ./stockfish ./stockfish-nnue 13 50

sf_base =  1472653 +/-   7293 (95%)
sf_test =  1491928 +/-   7661 (95%)
diff    =    19275 +/-   7154 (95%)
speedup = 1.30886% +/- 0.486% (95%)
```

closes https://github.com/official-stockfish/Stockfish/pull/5100

No functional change

src/search.h

@@ -25,8 +25,8 @@
 #include <cstddef>
 #include <cstdint>
 #include <memory>
-#include <vector>
 #include <string>
+#include <vector>
 
 #include "misc.h"
 #include "movepick.h"
@@ -37,6 +37,10 @@
 
 namespace Stockfish {
 
+namespace Eval::NNUE {
+struct Networks;
+}
+
 // Different node types, used as a template parameter
 enum NodeType {
     NonPV,
@@ -125,16 +129,20 @@ struct LimitsType {
 // The UCI stores the uci options, thread pool, and transposition table.
 // This struct is used to easily forward data to the Search::Worker class.
 struct SharedState {
-    SharedState(const OptionsMap&   optionsMap,
-                ThreadPool&         threadPool,
-                TranspositionTable& transpositionTable) :
+    SharedState(const OptionsMap&           optionsMap,
+                ThreadPool&                 threadPool,
+                TranspositionTable&         transpositionTable,
+                const Eval::NNUE::Networks& nets) :
         options(optionsMap),
         threads(threadPool),
-        tt(transpositionTable) {}
+        tt(transpositionTable),
+        networks(nets) {}
 
-    const OptionsMap&   options;
-    ThreadPool&         threads;
-    TranspositionTable& tt;
+
+    const OptionsMap&           options;
+    ThreadPool&                 threads;
+    TranspositionTable&         tt;
+    const Eval::NNUE::Networks& networks;
 };
 
 class Worker;
@@ -176,6 +184,7 @@ class NullSearchManager: public ISearchManager {
     void check_time(Search::Worker&) override {}
 };
 
+
 // Search::Worker is the class that does the actual search.
 // It is instantiated once per thread, and it is responsible for keeping track
 // of the search history, and storing data required for the search.
@@ -247,9 +256,10 @@ class Worker {
 
     Tablebases::Config tbConfig;
 
-    const OptionsMap&   options;
-    ThreadPool&         threads;
-    TranspositionTable& tt;
+    const OptionsMap&           options;
+    ThreadPool&                 threads;
+    TranspositionTable&         tt;
+    const Eval::NNUE::Networks& networks;
 
     friend class Stockfish::ThreadPool;
     friend class SearchManager;