change what exhaustive testing returns

Considering the network to be used by other use cases, or just not exhaustive testing, calling the function should return a 0-1 value for how accurate the test was. That way only check fitness needs to call which testing function it would like

Start by locating the exhaustive-testing function and the check fitness caller described in the issue, then inspect how the selected network and current test result are handled. Done means the testing call returns a 0-1 accuracy value and check fitness can choose the testing function without duplicating that selection.

Written by the indexing model from the issue text.