Make sure that tests always use the default settings.

[kfir4444]

Is your feature request related to a problem? Please describe. If a user tries to make test after adding some settings to their .arc folder, some tests might fail because of that. This is extremely important for developers, especially when trying to implement a new software, as the non- default settings may interfere with the testing and may lead to waste of time troubleshooting, waiting for CI's to converge, and so on.

Describe the solution you'd like I would like a flag like testing = False, that turns True if testing, and then only reads the default settings, skipping the .arc folder.

[alongd]

Good idea. We have testing in Scheduler: https://github.com/ReactionMechanismGenerator/ARC/blob/bfcef092458a8dd1b9806b786befb3f7569f2b1c/arc/scheduler.py#L154 you can make it do the settings trick