AGIPD: Fix dtypes and compression in output file
- Use the correct dtypes for trainId, pulseId, cellId & mask data
- Compress gain & mask data with gzip level 1 (as before)
- gzip compression is fairly slow: this adds about 30% to the correction time for the data I tested
- I will experiment with lzf compression, which may be faster
This is meant to fix a problem discussed starting here: https://git.xfel.eu/gitlab/detectors/calibration_workshop/issues/122#note_186424