Enable overwrite to receive a modified date

[matsvanes]

Scenario:
Preprocessing/source recon is done for all subjects, but now you changed the pipeline and have to redo it. You use overwrite=True, but the process fails at some point. A certain percentage of the files were processed, but not all.

I think it would be really practical if it were possible to enter e.g., overwrite='2025/02/23', and osl-ephys will then check what the last modified date is of the data, and only process when that date falls before the input date.