AZIP-2: Rollup Gating Contract

[just-mitch]

Summary

• Introduces AZIP-2, a proposal for a Gating Contract that enforces timelocks and rate-of-change constraints on rollup owner functions
• Critical actions (escape hatch changes, ownership transfers) get a 60-day timelock
• Operational parameters (rewards, fees, staking config) can execute immediately but with per-parameter rate-of-change constraints over time windows