Use std::filesystem

[matz-e]

Recent versions of nlohmann/json fail to compile with the
ghc::filesystem shim. Bump C++ stdandard, require a minimum Catch2
version, too.

[musicinmybrain]

This still seems like a good idea.

I tried this with Catch2 3.8.0, and I also needed to change each #include <catch2/catch.hpp> to #include <catch2/catch_all.hpp>. Then I needed to link the unittests target with Catch2::Catch2WithMain instead of Catch2::Catch2. After that, it seemed to work fine.

Are you planning to open a new version of this PR at https://github.com/openbraininstitute/libsonata at some point?

[matz-e]

@musicinmybrain thank you for testing!

Are you planning to open a new version of this PR at https://github.com/openbraininstitute/libsonata at some point?

I'm no longer involved with the associated project(s) - still get and respond to notifications when I can. But I am not going to port any PRs. Feel free to take this over!

The test logs expired, and I'm wondering if a switch to a newer manylinux would be required to get full support for std::filesystem à la neuronsimulator/nrn#1963 (comment) (mentions that newer images ship with GCC 14).