Improve ujson test coverage or clean up dead code
I've been spending some time cleaning up the integration with ujson in our source code. After enabling some debugging directives and running the test suite I noticed that there were quite a few places in objToJSON.c which were not being hit. This can point to either dead code or a lack of test coverage, so these can be whittled down.

In my own repo I have a branch of this where each of the items are commented with `// not hit in tests` which you can see here:

https://github.com/WillAyd/pandas/blob/dead-json/pandas/_libs/src/ujson/python/objToJSON.c

Planning to go through these individually and see what we can do. Extra set of eyes would certainly be welcome