Handle different scenarios when setting a new `UpdateEligibilityDelay`

[garyghayrat]

We should create an issue to think through what happens when this value is changed. I think it will cause problems, or at a minimum ambiguous situations. For example, if this is shortened, a bunch of scores immediately become qualified for updates. If it's lengthened, some scores may have updated that now wouldn't be qualified. We might need to switch to a model where the exact timestamp of the delay window ends is calculated and stored alongside score, based on whatever the delay is at the time of the update the makes it ineligible. But we don't have to tackle that here, we can think through it more carefully.

Originally posted by @apbendi in #24 (comment)

[garyghayrat]

Keeping track of the delay window for the rare case of the delay period changing feels a bit excessive. I think the example you gave fits the expectation of what should happen if the eligibilityDelay was updated, and the new delay not taking effect for certain delegates might cause more confusion imo.