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/uci.cpp

@@ -22,25 +22,25 @@
 #include <cassert>
 #include <cctype>
 #include <cmath>
+#include <cstdint>
 #include <cstdlib>
 #include <deque>
 #include <memory>
 #include <optional>
 #include <sstream>
 #include <vector>
-#include <cstdint>
 
 #include "benchmark.h"
 #include "evaluate.h"
 #include "movegen.h"
-#include "nnue/evaluate_nnue.h"
-#include "nnue/nnue_architecture.h"
+#include "nnue/network.h"
+#include "nnue/nnue_common.h"
+#include "perft.h"
 #include "position.h"
 #include "search.h"
 #include "syzygy/tbprobe.h"
 #include "types.h"
 #include "ucioption.h"
-#include "perft.h"
 
 namespace Stockfish {
 
@@ -48,17 +48,20 @@ constexpr auto StartFEN             = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKB
 constexpr int  NormalizeToPawnValue = 356;
 constexpr int  MaxHashMB            = Is64Bit ? 33554432 : 2048;
 
+
+namespace NN = Eval::NNUE;
+
+
 UCI::UCI(int argc, char** argv) :
+    networks(NN::Networks(
+      NN::NetworkBig({EvalFileDefaultNameBig, "None", ""}, NN::embeddedNNUEBig),
+      NN::NetworkSmall({EvalFileDefaultNameSmall, "None", ""}, NN::embeddedNNUESmall))),
     cli(argc, argv) {
 
-    evalFiles = {{Eval::NNUE::Big, {"EvalFile", EvalFileDefaultNameBig, "None", ""}},
-                 {Eval::NNUE::Small, {"EvalFileSmall", EvalFileDefaultNameSmall, "None", ""}}};
-
-
     options["Debug Log File"] << Option("", [](const Option& o) { start_logger(o); });
 
     options["Threads"] << Option(1, 1, 1024, [this](const Option&) {
-        threads.set({options, threads, tt});
+        threads.set({options, threads, tt, networks});
     });
 
     options["Hash"] << Option(16, 1, MaxHashMB, [this](const Option& o) {
@@ -80,14 +83,17 @@ UCI::UCI(int argc, char** argv) :
     options["SyzygyProbeDepth"] << Option(1, 1, 100);
     options["Syzygy50MoveRule"] << Option(true);
     options["SyzygyProbeLimit"] << Option(7, 0, 7);
-    options["EvalFile"] << Option(EvalFileDefaultNameBig, [this](const Option&) {
-        evalFiles = Eval::NNUE::load_networks(cli.binaryDirectory, options, evalFiles);
+    options["EvalFile"] << Option(EvalFileDefaultNameBig, [this](const Option& o) {
+        networks.big.load(cli.binaryDirectory, o);
     });
-    options["EvalFileSmall"] << Option(EvalFileDefaultNameSmall, [this](const Option&) {
-        evalFiles = Eval::NNUE::load_networks(cli.binaryDirectory, options, evalFiles);
+    options["EvalFileSmall"] << Option(EvalFileDefaultNameSmall, [this](const Option& o) {
+        networks.small.load(cli.binaryDirectory, o);
     });
 
-    threads.set({options, threads, tt});
+    networks.big.load(cli.binaryDirectory, options["EvalFile"]);
+    networks.small.load(cli.binaryDirectory, options["EvalFileSmall"]);
+
+    threads.set({options, threads, tt, networks});
 
     search_clear();  // After threads are up
 }
@@ -157,7 +163,7 @@ void UCI::loop() {
             std::string                f;
             if (is >> std::skipws >> f)
                 filename = f;
-            Eval::NNUE::save_eval(filename, Eval::NNUE::Big, evalFiles);
+            networks.big.save(filename);
         }
         else if (token == "--help" || token == "help" || token == "--license" || token == "license")
             sync_cout
@@ -218,7 +224,8 @@ void UCI::go(Position& pos, std::istringstream& is, StateListPtr& states) {
 
     Search::LimitsType limits = parse_limits(pos, is);
 
-    Eval::NNUE::verify(options, evalFiles);
+    networks.big.verify(options["EvalFile"]);
+    networks.small.verify(options["EvalFileSmall"]);
 
     if (limits.perft)
     {
@@ -283,9 +290,11 @@ void UCI::trace_eval(Position& pos) {
     Position     p;
     p.set(pos.fen(), options["UCI_Chess960"], &states->back());
 
-    Eval::NNUE::verify(options, evalFiles);
+    networks.big.verify(options["EvalFile"]);
+    networks.small.verify(options["EvalFileSmall"]);
 
-    sync_cout << "\n" << Eval::trace(p) << sync_endl;
+
+    sync_cout << "\n" << Eval::trace(p, networks) << sync_endl;
 }
 
 void UCI::search_clear() {