Add plugin receive loop & remote player state

Add a networking receive loop and in-plugin remote-player storage. Introduces F4TRemotePlayerState (header + implementation) to track assigned playerId and remote player snapshots with thread-safe access. Expands F4TNetworking to start/stop a background receive thread, parse newline-separated JSON packets (welcome, transform, disconnect), validate fields, update remote state, throttle logs, and handle socket/thread synchronization. Add nlohmann_json to xmake and plugin build. Update docs and dev log to reflect the new receive behavior and current prototype scope.

plugin/include/F4TRemotePlayerState.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <chrono>
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace F4T::RemotePlayerState
+{
+	struct RemotePlayerState
+	{
+		std::uint32_t playerId{};
+		float x{};
+		float y{};
+		float z{};
+		float angleZ{};
+		std::string movementType;
+		std::string cellId;
+		std::string worldspaceId;
+		std::optional<double> clientTime;
+		std::optional<double> serverTime;
+		std::chrono::steady_clock::time_point lastReceivedLocalTime{};
+	};
+
+	void SetAssignedPlayerId(std::uint32_t a_playerId);
+	std::optional<std::uint32_t> GetAssignedPlayerId();
+	bool IsAssignedPlayerId(std::uint32_t a_playerId);
+	void ClearAssignedPlayerId();
+
+	void UpdateRemotePlayer(RemotePlayerState a_state);
+	bool RemoveRemotePlayer(std::uint32_t a_playerId);
+	void ClearRemotePlayers();
+	std::vector<RemotePlayerState> GetRemotePlayerSnapshot();
+}