The best docs for nvidia are their own README: NVIDIA Accelerated Linux Graphics Driver README and Installation Guide
Note that’s for a specific driver version, the link will become outdated after a while.
There you can find what all the features do, including what persistenced is (a way to keep nvidia GPUs in servers “warm” at all times).
If it’s not obvious what an option does, I read the code and compare to the upstream docs. Many of the NixOS nvidia options are subtly broken, or at least variously inadvisable or misleading, so it’s worth reading a bit into what the options are ultimately supposed to effect (and double check they actually do that).
As for mkDriver, yeah, it’s only documented as far as it needs to be. It won’t explain what the various args do, the names just match specific features which you have to independently understand.