Add SimConnect_SubscribeToSystemEvent handling

[eozdil174]

Summary

Adds SimConnect_SubscribeToSystemEvent handling to the SimConnectClient

Usage example:

// The EventId can be any number
client.SystemEventReceived += (sender, e) =>
{
    switch (e.EventId)
    {
        case 100:
            Console.WriteLine("Simulator is running or a flight has started!");
            break;
    }
}

// Subscribe to the event (will start listening immediately)
await client.SubscribeToEventAsync("4sec", 100);

Changes Made

• Added new SimConnectClient.SubscribeToEventAsync method for event subscription
• Added a basic Test to check the functionality of the new Event system

Additional Information

Some background on why I've implemented this:

I am a developer for a Virtual airline and have started using your library during my refactoring away from FSUIPC for Sim communication, we check for when a user has paused their sims to various actions. While implementing the new code I've noticed the only way to reliably check the pause state on MSFS is to use these Simconnect System Events. Which wasn't supported from what I could see so I decided to make a small PR to add the implementation.

Let me know if anything needs changing or if there is any points you would like to discuss.

Author Information

Discord Username: eoz.dll

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Checklist:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

[greptile-apps]

Greptile Summary

• Adds SimConnect system event subscription functionality to enable monitoring of simulator state changes like pause/unpause events through a new SubscribeToEventAsync method and SystemEventReceived event
• Introduces SimSystemEventReceivedEventArgs class for strongly-typed system event data handling and integrates system event processing into the existing message handling pipeline
• Includes comprehensive test coverage with new SystemEventSubscriptionTests class and command-line filtering option for system event tests

Important Files Changed

Filename	Overview
src/SimConnect.NET/SimConnectClient.cs	Core implementation adding SubscribeToEventAsync method, SystemEventReceived event, and ProcessSystemEvent message handling
src/SimConnect.NET/Events/SimSystemEventReceivedEventArgs.cs	New EventArgs class providing strongly-typed container for system event data with EventId and Data properties
tests/SimConnect.NET.Tests.Net8/Tests/SystemEventSubscriptionTests.cs	New test class validating system event subscription functionality using "4sec" system events
tests/SimConnect.NET.Tests.Net8/Tests/TestRunner.cs	Updated test runner to include SystemEventSubscriptionTests and added --test-events command line option

Confidence score: 4/5

• This PR is safe to merge with minor review recommended due to well-structured implementation following existing patterns
• Score reflects solid architecture, proper error handling, and comprehensive testing, with only minor documentation formatting issues found
• Pay close attention to SimSystemEventReceivedEventArgs.cs for the trailing period in XML comment that should be removed for consistency

[greptile-apps]

Additional Comments (3)

1. src/SimConnect.NET/Events/SimSystemEventReceivedEventArgs.cs, line 11-12 (link)

   syntax: Line 11 has a trailing period after 'identifier and' in the XML comment

2. tests/SimConnect.NET.Tests.Net8/Tests/SystemEventSubscriptionTests.cs, line 31-40 (link)

   style: Event handler should be unsubscribed in a finally block to prevent memory leaks in case of exceptions

3. src/SimConnect.NET/SimConnectClient.cs, line 358 (link)

   syntax: The return type description says 'A task representing the event' but should say 'A task representing the subscription operation'

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