change: move apis to LuaThreadAccess to validate context

[Akeit0]

The following code now works safely.

state.Environment["dostring"] = new LuaFunction("dostring",
    async (context, ct) =>
    {
        var source = context.GetArgument<string>(0);
        return context.Return(await context.Access.DoStringAsync(source, source, ct));
    });
 
var result = await state.DoStringAsync("""return dostring("return 1")""");

@nuskey8
What do you think about the naming of LuaThreadAccess and LuaState.TopLevelAccess?
TopLevelAccess is the one that only has access when the callstack is empty.

[Akeit0]

Alternatives to toplevel are entry, root, and idle.

[nuskey8]

Looks good! I'd like to make some final adjustments to the API, but this should be enough for now.