rsb-23/dateutilx ? reverse-engineered prompt

Build me a Python library that extends the standard datetime tools in a really practical way, like a modern rewrite of python dateutil for current Python versions only.

I want it to make date handling easier with things like relative date math, recurring schedules, flexible date parsing, timezone handling, and Easter date calculations. It should feel easy to import and use in normal Python code, with a clean API and good docs. Please include solid tests for the main behaviors, and make sure the examples in the README actually work.

If anything is unclear from the old project, look up the current docs online and match the expected behavior as closely as makes sense, but keep the code focused on supported modern Python.