Add Source Generator

[nuskey8]

We need a source generator to generate function definitions and userdata, which will reduce the boiler code and provide optimal implementations.

[nuskey8]

API proposal

LuaFunction

var state = LuaState.Create();
state.OpenLibrary<LuaCommands>();

[LuaLibrary]
public partial class LuaCommands
{
    [LuaFunction]
    public double Foo(double a, double b)
    {
        return a + b;
    }

    [LuaFunction]
    public async ValueTask<double> FooAsync(double a, double b, CancellationToken cancellationToken = default)
    {
        await DoSomethingAsync(cancellationToken);
        return a + b;
    }
}

LuaObject

var state = LuaState.Create();
var results = await state.DoStringAsync(
"""
local foo = Foo.new(1, "hello!")
foo.alpha = 10
foo.beta = "hey!"
return foo
"""
);

var foo = results[0].Read<Foo>();

[LuaObject]
public partial class Foo
{
    [LuaConstructor]
    public Foo(double alpha, string beta)
    {
        Alpha = alpha;
        Beta = beta;
    }

    [LuaMember("alpha")]
    public double Alpha { get; set; }

    [LuaMember("beta")]
    public string Beta { get; set }
}

[nuskey8]

#39