Prevent overlapping referral program editions

[lightwalker-eth]

Goal

Simplify and constrain the edge cases in our data model by making it impossible for a single referral to be associated with multiple referral program editions.

Spec

1. Each referral should be associated with 0 or 1 referral program editions and never 2+.
2. To enforce this, suggest that we add more invariant checks to how a referral program config set is defined. If we enforce that for a specific registryId no two referral program editions can overlap in time then we achieve this constraint. When implementing this invariant, please take special note of how the start / end time for an edition is inclusive.

[coderabbitai]

⚠️ Possible Duplicate Issue(s)

• Provide detailed referral award accounting #1797

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