fix: add deduction guides for Struct from std::tuple (#525)

* Types.h: add deduction guides for Struct from std::tuple

C++23 changed the generation of implicit deduction guides. This causes
the compiler to also see deduction guides for std::tuple as candidates
for sdbus::Struct.
Because of the competing guides the compiler doesn't know which one to pick.

This seems to be implemented from gcc 15 on and is thus causing breakage there.

To fix this we need to add explicit deduction guides when std::tuple is passed
to sdbus::Struct.

fixes #524

* refactor: remove std::decay_t wrapper

We need to be able to create sdbus::Structs
with element types being references.

---------

Co-authored-by: Stanislav Angelovič <stanislav.angelovic@protonmail.com>

Author: heinemml

include/sdbus-c++/Types.h

@@ -177,6 +177,12 @@ namespace sdbus {
     template <typename... _Elements>
     Struct(_Elements...) -> Struct<_Elements...>;
 
+    template <typename... _Elements>
+    Struct(const std::tuple<_Elements...>&) -> Struct<_Elements...>;
+
+    template <typename... _Elements>
+    Struct(std::tuple<_Elements...>&&) -> Struct<_Elements...>;
+
     template<typename... _Elements>
     constexpr Struct<std::decay_t<_Elements>...>
     make_struct(_Elements&&... args)