refactor: extract toHexString utility, more color constants, final cast cleanup

Add core::toHexString() utility in logger.hpp to replace 11 duplicate
hex-dump loops across world_packets, world_socket, and game_handler.
Add kColorBrightGreen/kColorDarkGray constants in game_screen.cpp
replacing 26 inline literals. Replace remaining ~37 C-style casts in
16 files. Normalize keybinding_manager.hpp to #pragma once.

include/core/logger.hpp

@@ -7,6 +7,8 @@
 #include <fstream>
 #include <chrono>
 #include <atomic>
+#include <cstdio>
+#include <cstdint>
 
 namespace wowee {
 namespace core {
@@ -144,6 +146,17 @@ private:
     } \
 } while (0)
 
+inline std::string toHexString(const uint8_t* data, size_t len, bool spaces = false) {
+    std::string s;
+    s.reserve(len * (spaces ? 3 : 2));
+    for (size_t i = 0; i < len; ++i) {
+        char buf[4];
+        std::snprintf(buf, sizeof(buf), spaces ? "%02x " : "%02x", data[i]);
+        s += buf;
+    }
+    return s;
+}
+
 } // namespace core
 } // namespace wowee