`Observable_interval` function added and `months_observable` aliased
Added a generic version months_observable called observable_interval. I also aliased months_observable to maintain backwards comparability, and help clean the code base. weeks_observable and days_observable aliases were also added; I felt it appropriate with months_observable remaining in the code. Lastly, I fixed a small issue with the "_current_year_time_range" as I noticed that it was not calculating visibility for December 31st in its current form.
Let me know if there is anything you think might need changed.
I have fixed the code style issues that were preventing check completion.
I have correct the issues that were indicated in the workflow.
This is looking good. Could you please add tests for the new methods days_observable and weeks_observable?