[newchem-cpp] Adjust API tests (factor out preset-fixtures and add basic ratequery tests)

[mabruzzo]

To be reviewed after #469

---

This PR basically does 2 things:

1. If factors out some logic from the test_ghost_zone.cpp tests and polishes it. This logic implements a fixture that:

   • initializes chemistry_data, chemistry_data_storage, and code_units using some "presets" before a test
   • obviously cleans up these particular allocations at the end of the test
   • the basic motivation is that there are a lot of really simple tests of Grackle's C API that we could write where we don't necessarily care about the specifics of exactly how Grackle is configured (as long as the configuration is semi-reasonable).

2. Uses this machinery to help implement some basic tests for the ratequery API. (A bunch of these tests were informed by a PR that I'm working on in parallel)

Note

Aside: while the IteratorAdaptor machinery seems a little like its overkill, it comes in handy for iterating over the ratequery accessible rate names in this PR and subsequent PRs.
It also lets us implement iteration over dynamically-accessible chemistry parameters (e.g. see the tests introduced in #470)