Add creation date as parameter, allow both dates and offsets as values

[bkleinen]

Goal

• As a user of things
• I want to see the tasks completed today, and some statistics on the tasks created in this year
• so that

Suggested approach
In order to achieve this goal I suggest to
add created_at as possible date parameter.
Also, it would be nice to be able to use offsets or dates for all date parameter.

Additional context

I was quite confused by the examples combining completed with last,
as this shows the completed tasks created within the last week, not completed in the last
week, as last uses the creationDate rather than the stop_date:

(as I wanted to see the tasks completed this day, no matter when they were created)

things.last('1w', status='completed')
things.completed(type='to-do', last='1w')

[mikez]

Are you aware of stop_date?

things.completed(type='to-do', stop_date='>=2025-08-24')

Looking over this .last API, I agree it's confusing why it only should mean "created" and why not modified or completed or stopped or something else. What makes this slightly more complex is that in Things-DB-land status only has a certain set of values {'incomplete', 'completed', 'canceled'}. The concept of created, modified, started, stopped is something else and modeled in other ways.