This function was writing the rewards (self.utilities) by converting
them to integers.

Error was that some filepaths for the read and write tests were using
hardcoded paths i.e. if I execute `pytest` from `home/user`, while the
test directory is at `home/user/gtnash/test`, the failing tests would look
for `filestest/` in `home/user` instead of the test directory. Using
`pathlib` to resolve the correct path at runtime solves this.

binder: enable

See merge request !11

use tag stable

Test are not update, use of Y is still the standart