Fix luaref returned from call<>()

[kunitoki]

This pull request improves the handling of Lua function return values as C++ tuples and adds a new test case to verify support for tuples containing LuaRef objects. The main change refactors how tuple results are decoded from the Lua stack to be more robust and efficient.

Tuple result decoding improvements:

• Refactored decode_tuple_result in Invoke.h to first collect all stack elements into a tuple of std::optional values, then check for errors and construct the result tuple in a single step. This streamlines error handling and avoids partially constructed tuples.

Testing enhancements:

• Added a new test CallReturningTupleWithLuaRef in LuaRefTests.cpp to verify that Lua functions returning a tuple with a table (as a LuaRef) are correctly handled, including checking table contents.