Specify `out_files` correctly/compatible with multiple runs in _05b_sync_eyelink.py

[jschepers]

Currently, the specification of out_files in _05b_sync_eyelink.py will only work for a single run because it's hard-coded to use the first filename (which means run 1) in the list:

    bids_basename = raw_fnames[0].copy().update(processing=None, split=None, run=None) #TODO: Do we need to remove the run here?

mne-bids-pipeline/mne_bids_pipeline/steps/preprocessing/_05b_sync_eyelink.py

Line 174 in 16c15b3

bids_basename = raw_fnames[0].copy().update(processing=None, split=None, run=None) #TODO: Do we need to remove the run here?

Possible solutions/alternatives:

1. For now just throw an error in the case of multiple runs (since we only have one run in our experiment). Code from Bene:

if len(et_fnames)>1:
    error("support for more than one run with EyeLink integration currently not implemented (it's not necessarily hard to do, but we simply didnt do it :)")

2. Move the out_files creation in the loop over runs.

3. Adapt the sync_eyelink function to work on a single run and move the loop over runs to main (as it is done in other pipeline scripts) using the get_run_tasks function.e.g. https://github.com/s-ccs/mne-bids-pipeline/blob/0a870021e6ad61b2d55d1ddd8dbf6eb83bb1ba9d/mne_bids_pipeline/steps/preprocessing/_08a_apply_ica.py#L296C1-L300C14