Adds check for active simulator before commands

Implements a check to ensure a simulator is active before processing commands.

This prevents errors and unexpected behavior when commands are sent without an active simulator. The check is performed at the beginning of the command parsing, and logs an error if no simulator is active, returning an empty JSON object.

server/simulators.cpp

@@ -151,6 +151,11 @@ std::vector<std::string> Simulators::list_simulators() const
     return names;
 }
 
+bool Simulators::is_not_active() const
+{
+    return this->m_current_simulator.empty();
+}
+
 Simulator_base *Simulators::invoke_active_simulator()
 {
     std::lock_guard<std::mutex> lock(m_mutex);