Including the code below if anyone is curious. I managed to get a 9 zero hash in under an hour on a M2 Mac Mini using it. Its only about ~3.3 MH/s which is not very impressive, but it was very easy to write.
https://gist.github.com/boyter/8600199cc6f4073dc9da380f3224f...
I suppose the next step for me would be to make use of the GPU, which is a much better fit for this job and I'm sure would increase my hash rate by orders of magnitude, but I researched it for a bit and running code on the GPU on a Mac is cumbersome to say the least.
It gets around 232.5 MH/s on the M1 Max. There's also an optimization that exploits the fact that SHA256 is incremental, so the state for the common prefix could be pre-computed and then copied and only updated with the variable part. This yields around 30% performance boost.