Header shortest_paths.hpp adds dependency on fmt/format.h

[akrzemi1]

This library should not depend on fmt/format.h, especially that on MSVC there is no reason to include it when we have <format>.

[pratzl]

I chose to use a recent version of fmt to provide the latest capabilities in the library, as they continue to improve it, without requiring us to bump graph-v2 to use C++23. print() and println() are obvious things, but there are other features I can't recall off the top of my head.
Is this causing you any problems?

[akrzemi1]

In my environment, I do not have the {fmt} library. That this should perevent me from doing the Shortest Paths algorithm is strange.

I tried to see if this is still the case, but I can see that the file shortest_paths.hpp is gone. I tried graph/algorithm/common_shortest_paths.hpp, but only through including it, I get error C2760 at line:
https://github.com/stdgraph/graph-v2/blob/master/include/graph/algorithm/common_shortest_paths.hpp#L18

This is about the undefined identifier is_arithmetic_v, and a bunch of other identifiers in this file (like edge_reference_t). It looks like they require the namespace prefix.

[pratzl]

CMake should be downloading the {fmt} library if you "Delete Cache and Reconfigure".
There's now dijkstra_shortest_paths.hpp and bellman_ford_shortest_paths. This is similar to how Boost Graph does these algorithms.
In the move from std::graph to the graph namespace, I added the using statements in graph_using.hpp to make things look cleaner. I don't know if this is the best idea, but I find it improves readability for myself. I've added an #include for that in common_shortest_paths.hpp so people won't get that error. It will be in the next push, hopefully this week.