Fix pandas warning
This warning just popped up:
src/calimag/parsers.py:662: FutureWarning: Series.__getitem__ treating keys as positions is deprecated. In a future version, integer keys will always be treated as labels (consistent with DataFrame behavior). To access a value by position, use `ser.iloc[pos]`
if start_time_pd > timestamps_pd[0]:
Versions:
hdmf==3.11.0
numpy==1.26.2
pandas==2.1.3
pynwb==2.5.0