The previous test claimed to verify that all possible outputs
are sampled, but it didn't. This commits fixes this issue
by actually computing all possible combinations.
However, to accomplish this we needed to add itertools as a test
dependency. Otherwise we'd have to implement our own way of
generating the Cartesian product of an arbitrary number
of sets.
This introduces functionality for creating strategies for matrices and
vectors, as well as an implementation of Arbitrary.
Strategies for the geometric types (Point3, Quaternion etc.) are not
currently part of this contribution.
The current strategy implementation for matrices has some limitations
that lead to suboptimal shrinking behavior. This is documented in the
module-level docs, with some additional comments in the code.
