Write `fTOA` fields for Timepix3 data

[Vindaar]

We parse the fTOA data in the parse_raw_tpx3.nim file here:

https://github.com/Vindaar/TimepixAnalysis/blob/master/Analysis/ingrid/parse_raw_tpx3.nim#L275-L281

but we don't actually write them over to the HDF5 file in raw_data_manipulation. This still needs to be finished. @magruber took some data with the extented mode active. Need to use one of those files for testing (and write a test case, cough).