Fix sequencer event_table parsing

[DJDuque]

If the first sequence has an empty event table, polars makes the event_table column have a type list(list(str)) instead of the correct list(struct). See e.g. run 9793

[DJDuque]

Fixed since #18, but remove the _asdict() (https://github.com/ALPHA-g-Experiment/analysis-scripts/blob/main/bin/sequencer.py#L37) once the issue is fixed in polars upstream (remember to update the requirements.txt version).