TST: move easter to own file and parameterize (#27085)
- [ ] xref #27085 (chips away at, yes)
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

* https://github.com/pandas-dev/pandas/pull/42284 
* https://github.com/pandas-dev/pandas/pull/42896 
* https://github.com/pandas-dev/pandas/pull/42909
* https://github.com/pandas-dev/pandas/pull/42930
* https://github.com/pandas-dev/pandas/pull/42932
* https://github.com/pandas-dev/pandas/pull/42952
* https://github.com/pandas-dev/pandas/pull/42989