Reward Calc should report consistent results across validators

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Problem:

• The issue is that the blocknumber/timestamp can be different across users, within a small frame of time. We could perhaps do a mathy solution, round down the blocknumber/timestamp, or perhaps create an artifact/checkpoint.csv that we can distribute to validators, so everyone knows where to start/end.
• We're going to add the candidate solutions to a ticket, research this a bit more, and figure out some better candidate solutions so we can move forward with next steps.

Candidate Solutions

Candidate A

• Implement a math-based solution that calculates a consistent start/end block across all validators
  Candidate B
• Implement a rounding/blocknumber solution where by rounding down, we reduce the likelyhood of getting different results
  Candidate C
• Implement an artifact/csv that is distributed to validators so there are clear start/end blocks/time, eliminating any room for error

DoD:

• Explore candidate solutions further and asses which one we'll use
• Roughly estimate the effort/complexity and agree on it before signing off
• Validators report consistent results that are low variance