Allow users to configure whether to overwrite results files

[alexdewar]

Results files are currently written to muse2_results/{model_name}. If there are any files in there already, they will be overwritten.

We should allow users to choose whether or not to overwrite the files. I'd suggest that by default, we should raise an error if the output folder already exists, unless the user provides a command-line argument to overwrite it (e.g. --overwrite)¹. I don't think we should make this configurable in settings.toml as it would make it too easy to accidentally overwrite data.

Another possibility is that we could append a timestamp to the folder name (i.e. muse2_results/{model_name}_{timestamp}) to reduce the chance of collisions. We could make this pattern configurable in settings.toml (see also #370) using some kind of formatted string (for which we'll probably need to add a crate which can do dynamic string formatting like this).

Footnotes

1. Note: we should make sure to delete the contents of the folder before we start the run, so that we don't end up with a mix of files from the previous and current runs. ↩