Add __len__ to cartesian_product_iterator and fix a bug with an empty list input.
Trac #13428: review patch for length and cardinality of cartesian products
Add a max_runs keyword to Sage's unit tests and update tests with runtime quadratic or cubic in the number of elements.
fixed the bounds for the tests and some of the test cases
Merge branch 'padic_review' of github.com:saraedum/padic-review into padic_review