feat: add FakeConVar class

[roflmuffin]

Proposed usage, in your main plugin class:

public FakeConVar<bool> TestConVar = new ("my_allow_bool", "Allow the thing", defaultValue: true);
public FakeConVar<int> IntConvar = new ("my_allow_int", "Allow the thing", defaultValue: 20, new RangeValidator<int>(0, 5));
public FakeConVar<string> StrConvar = new ("fake_convar_str", "Allow the thing"));

... later on in plugin load:

TestConVar.ValueChanged += (sender, value) =>
{
    Logger.LogInformation("TestConVar value changed to {Value}", value);
};

Full Example Plugin

public class WithFakeConvarsPlugin : BasePlugin
{
    public override string ModuleName => "Example: With Fake Convars";
    public override string ModuleVersion => "1.0.0";
    public override string ModuleAuthor => "CounterStrikeSharp & Contributors";
    public override string ModuleDescription => "A simple plugin that registers some console variables";
    
    // FakeConVar is a class that can be used to create custom console variables.
    // You can specify a name, description, default value, and custom validators.
    public FakeConVar<bool> BoolCvar = new("example_bool", "An example boolean cvar", true);
    
    // Range validator is an inbuilt validator that can be used to ensure that a value is within a certain range.
    public FakeConVar<int> ExampleIntCvar  = new("example_int", "An example integer cvar", 10, flags: ConVarFlags.FCVAR_NONE, new RangeValidator<int>(0, 100));
    
    public FakeConVar<float> ExampleFloatCvar = new("example_float", "An example float cvar", 10, flags: ConVarFlags.FCVAR_NONE, new RangeValidator<float>(5, 20));
    public FakeConVar<string> ExampleStringCvar = new("example_string", "An example string cvar", "default");

    // Replicated, Cheat & Protected flags are supported.
    public FakeConVar<float> ExamplePublicCvar = new("example_public_float", "An example public float cvar", 5,
        ConVarFlags.FCVAR_REPLICATED);
    
    // Can only be changed if sv_cheats is enabled.
    public FakeConVar<float> ExampleCheatCvar = new("example_cheat_float", "An example cheat float cvar", 5,
        ConVarFlags.FCVAR_CHEAT);
    
    // Protected cvars do not output their value when queried.
    public FakeConVar<float> ExampleProtectedCvar = new("example_protected_float", "An example cheat float cvar", 5,
        ConVarFlags.FCVAR_PROTECTED);
    
    // You can create your own custom validators by implementing the IValidator interface.
    public FakeConVar<int> ExampleEvenNumberCvar = new("example_even_number", "An example even number cvar", 0, flags: ConVarFlags.FCVAR_NONE, new EvenNumberValidator());

    public FakeConVar<int> RequiresRestartCvar = new("example_requires_restart", "A cvar that requires a restart when changed");
    
    public override void Load(bool hotReload)
    {
        // You can subscribe to the ValueChanged event to execute code when the value of a cvar changes.
        // In this example, we restart the game when the value of RequiresRestartCvar is greater than 5.
        RequiresRestartCvar.ValueChanged += (sender, value) =>
        {
            if (value > 5)
            {
                Server.ExecuteCommand("mp_restartgame 1");
            }
        };
        
        RegisterFakeConVars(typeof(ConVars));
    }
}

All FakeConvar fields on your plugin class will be automatically registered, but if you want to register some from another class you can do it using plugin.RegisterFakeConVars(myOtherClass), similar to event attributes.