Add fuzz testing for file formats

[ghutchis]

The latest seems to be fuzztest:
https://github.com/google/fuzztest/blob/main/doc/quickstart-cmake.md
https://github.com/google/fuzztest/blob/main/doc/use-cases.md

I'd suggest adding fuzz tests for all the "native" file formats, e.g:

• cjson
• cml
• xyz
• pdb
• sdf

Obvious many of the other formats should also get fuzz testing, but that's a good start.

[ghutchis]

Here's an example of loading files from a corpus:
https://github.com/google/fuzztest/blob/main/doc/fuzz-test-macro.md#loading-seed-inputs-from-a-directory

It looks like this requires separate directories for each file type.