`gcc`: a lot of `-Werror=shadow` related errors for the `Hello, world !` example

Example at https://github.com/NVIDIA/stdexec/blob/8bc7c7f06fe39831dea6852407ebe7f6be8fa9fd/include/stdexec/__detail/__basic_sender.hpp#L408:

/workspaces/.../external/stdexec/include/exec/../stdexec/__detail/__basic_sender.hpp: In member function 'void stdexec::__detail::__op_state<_Sexpr, _Receiver>::start() &':
/workspaces/.../external/stdexec/include/exec/../stdexec/__detail/__basic_sender.hpp:408:15: error: declaration of 'using __tag_t = using __tag_t = typename decltype (__mdecay<_Ty>)::__f<_Ty>::__desc_t::__tag' shadows a member of 'stdexec::__detail::__op_state<_Sexpr, _Receiver>' [-Werror=shadow]
  408 |         using __tag_t = typename __op_state::__tag_t;
      |               ^~~~~~~
/workspaces/.../external/stdexec/include/exec/../stdexec/__detail/__basic_sender.hpp:382:13: note: shadowed declaration is here
  382 |       using __tag_t = typename __desc_t::__tag;
      |             ^~~~~~~

I guess that this should be resolved, as it might hide bugs ?

Start with include/stdexec/__detail/__basic_sender.hpp, especially the declarations around lines 382 and 408 shown in the report, and build the Hello, world! example with GCC and -Werror=shadow. Find the other shadow diagnostics in the example build and resolve them without changing behavior; done means the example builds without these errors.