Add modular test contract for BinaryEligibilityOracleEarningPowerCalculator

[alexkeating]

Description

• Add tests for bumping earning power
• Make sure address has 100% earning power
• Test for 0 and 100% earning power (in the case where earning power does not resolve to 100%, it will break existing tests. Therefore, we need separate tests for cases where earning power resolves to 0)