feat: Add support for "week" as a valid unit of time in time strings

[ChristopherJHart]

This PR fixes #5135 and stands as a potential implementation for a "week" as a valid unit of time in a time string.

Documentation was updated to indicate that a "week" is now a valid unit of time. Furthermore, unit tests were also added to ensure backwards compatibility. I should call out that one of the unit tests ensuring invalid formats raise an exception needed to be modified from w to y in order to pass. I think the intent of this unit test was to ensure that units of time must be sorted (e.g. days, then hours, then minutes, etc.) and not reversed/arbitrary (minutes, then weeks, then days, etc.). However, if I misinterpreted that and need to modify the unit tests somehow, let me know!