Combine impl CircuitData blocks (#13336)

The `CircuitData` struct had two `impl CircuitData` blocks, one before the
pymethods and the other after. While there is nothing wrong with doing
this it is a bit confusing because the difference between the blocks is
not clear. I expect this was caused by the size of the file and people
missed that it already existed and we ended up with duplicates. This
commit recombines the two blocks, opting to use the one after the
pymethods as it was larger.