* refactor: return date/datetime for due date
* fix: explicitly set due date on vTODO component
Using `set_due` automatically handles converting the Python-native
date/datetime values to the correct representation required by RFC5545.
* fix: fix tests with changed due date handling
* fix: item.due may not be a str
* refactor: keep local timezone of due datetime
* refactor: reorder import statement
To make ruff happy.
* fix: fix false-positive mypy error
063ac53f01