Create single-threaded concurrent caller example about autobahn-cpp

[i94matjo]

After some digging into boost(!) the exact same functionality as suggested in #203 can be accomplished by defining BOOST_THREAD_PROVIDES_EXECUTORS and use boost::inline_executor as executor on the future continuations. So #203 is totally unnecessary, Well, you live and learn... If that's the way we end up using remains to be seen...

[oberstet]

interesting! thanks for dropping this info here.

yeah, these features still seem to be very newish and lacking in docs. historically (when we started autobahnc++), even mere futures in boost were mildly problematic;) things have improved these days ..

anyways, fwiw, besides the boost implementation of executors, there seems to be https://github.com/chriskohlhoff/executors (I haven't used it). but in general, yep, that executors c++23 feature looks promising .. eg all this stuff https://cor3ntin.github.io/posts/executors/

note: executors are not needed to implement the example as described in the issue here