Fixed #22579 -- Corrected validation for email to reject trailing slash

Thanks to Claude Paroz for the report and patch and Tomasz
Paczkowski for the review.
Fixed #22490 -- removed obsolete ComplexFeed class from syndication_tests

It was previously used in a test that was deprecated and then removed, this cruft can be removed now.
Removed an unused import
Fixed #22531 -- Added tree.Node.__repr__ and tests for the class.

While Node class has a useful `__str__`, its `__repr__` is not that
useful. Added a `__repr__` that makes use of the current `__str__`.
This is especially useful since the more popular `Q` class inherits
`tree.Node`. Also created new tests that cover most of `Node` class
functionality.