S人ving Privàte Ryän

Fixes problems with non-ASCII characters in paths. Fixes #3424.

Changes
- Bump the minimum supported Clang version to 11 to support std::filesystem
- Use std::optional for empty values instead of string sentinels like "None"
- Remove the FixedString class
- Move the EvalFile network path from the network struct to the engine
- Simplify parts of the command-line handling
- Remove the old dual-net logic from export_net
- And ofc we now support non-ascii paths for windows

Behavior Change
- Because the EvalFile is no longer part of the network, it won't be included in the hashing, thus the network sharing is no longer dependent on the EvalFile path
- As a result, if the binary version and network are the same, changing only the EvalFile location will now reuse the same shared network

This also fixes a master bug where:

```
export_net None
setoption name EvalFile value None
export_net None
Failed to export a net
```

would fail on the second export. With this patch, the second export succeeds.

Quick Fishtest Check that nets load like normal.
https://tests.stockfishchess.org/tests/view/6a455593f97ff95f787954da

<img width="833" height="1137" alt="image" src="https://github.com/user-attachments/assets/fffee63b-c63a-4d5e-b13d-87d58bc28c88" />

closes https://github.com/official-stockfish/Stockfish/pull/6937

No functional change

Co-authored-by: anematode <timothy.herchen@gmail.com>

src/uci.cpp

@@ -26,6 +26,7 @@
 #include <optional>
 #include <sstream>
 #include <string_view>
+#include <filesystem>
 #include <utility>
 #include <vector>
 
@@ -63,9 +64,9 @@ void UCIEngine::print_info_string(std::string_view str) {
     sync_cout_end();
 }
 
-UCIEngine::UCIEngine(int argc, char** argv) :
-    engine(argv[0]),
-    cli(argc, argv) {
+UCIEngine::UCIEngine(CommandLine cli_) :
+    engine(cli_.argc > 0 ? std::optional{path_from_utf8(cli_.argv[0])} : std::nullopt),
+    cli(std::move(cli_)) {
 
     engine.get_options().add_info_listener([](const std::optional<std::string>& str) {
         if (str.has_value())
@@ -85,6 +86,7 @@ void UCIEngine::init_search_update_listeners() {
 }
 
 void UCIEngine::loop() {
+    set_console_utf8();
     std::string token, cmd;
 
     for (int i = 1; i < cli.argc; ++i)
@@ -151,10 +153,11 @@ void UCIEngine::loop() {
             sync_cout << compiler_info() << sync_endl;
         else if (token == "export_net")
         {
-            std::pair<std::optional<std::string>, std::string> file;
+            std::optional<std::filesystem::path> file;
+            std::string                          filename;
 
-            if (is >> file.second)
-                file.first = file.second;
+            if (is >> filename)
+                file = path_from_utf8(filename);
 
             engine.save_network(file);
         }
@@ -171,7 +174,7 @@ void UCIEngine::loop() {
             sync_cout << "Unknown command: '" << cmd << "'. Type help for more information."
                       << sync_endl;
 
-    } while (token != "quit" && cli.argc == 1);  // The command-line arguments are one-shot
+    } while (token != "quit" && cli.argc <= 1);  // The command-line arguments are one-shot
 }
 
 Search::LimitsType UCIEngine::parse_limits(std::istream& is) {