Pull Request Check List

Changed

• Relaxed dependency constraints. #760
• The testing helpers are now optional and must be opted-in via the test extra. #778

Fixed

• Removed remaining mentions of periods instead of intervals. #757
• Fixed the behavior of the week_of_month property for edge cases in January and December. #774
• Fixed the handling of the fold attribute when deep-copying a DateTime instance. #776
• Fixed errors where hours and days were not handled properly when adding durations. #775
• Fixed errors where hours and days were not handled properly when adding durations. #775