Run verifyproblem on all examples in CI

[gkreitz]

Looks like unfortunately this will need to stop testing with pypy in CI, as pip install of nh3 fails with:

  × Preparing metadata (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> [4 lines of output]
      Checking for Rust toolchain....
      Rust not found, installing into a temporary directory
      Python reports SOABI: pypy39-pp73
      Unsupported platform: pp73

nh3 does not seem to provide binary wheels for pypy, and I gave up on trying to debug that build issue. Instead of pypy, we now test with CPython 3.11, 3.12, and 3.13 to get better coverage there. I'm guessing the vast majority of users will use CPython to run problemtools anyway.

Fixes #325

[pehrsoderman]

Leftover debugging?

[gkreitz]

Debugging yes. Not quite leftover though, I felt it was sort of reasonable to leave behind (costs nothing, and may come in handy again in the future).

[pehrsoderman]

Do you want me to remove the requirement to build on pypy?