Previously the `once_per_instance` used the output of `__repr__` to
identify the class of where the decorated method was called from. For
classes that override this method to produce the same output for
different instances of the same class this caused different instances to
be mistakenly treated as one. Now use the hash of the containing class
instead of the string representation and update the tests to catch this
error.
Previously there was no differentiation between the same method at different
inheritance levels, therefore using the once_per_instance_decorator with super call would
prevent the super call from executing as they were considered the same
instance.
Tests now reside in the root of the repo, rather than in wa package.
This means they will no longer packaged and installed in user
deployments (they're only useful for developers).
